In what ways is the word “work” as used in everyda:a(x.xjwb75vzq kf w n wtywd.;mw )kw599,wcy language the same as that defined in physics? In nfdmww ;,:95. wztk(kvaw xbcww.w5 y)qj7 x9what ways is it different? Give examples of both.

Can a centripetal force ever do work on an obd- djiyfg *66m 4airr8ject? Explain.

Can the normal force on an object ever do lk4lq k mojp.5cs 3g22work? Explain.

A woman swimming upstr9g5 . zyhvi)0apclre)eam is not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats,pc9r)zev.0) ylag i5h is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: cn1 zq*z/cfc mu;g l,naj6;1x Consider what happens to thzm,jcu*qa1 zcf1;ncl6/n g x; e dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doing n.h :ahg jqwj2u o/7l8no wo2q/78 . u wnhgaljo:hjrk?

You have two springs that are identical except that spring l is 9 v*n3ig fl1vbstiffer than spring 2 i f3b lgv1vn*9$(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block thav9egc6k)fopy os1 *4wy w up.j m*jo/(t is free to slide on a frictionless surface (Fig.6-30). The block starwfm/j9puv64)o*eo j(y y1pk.owg sc* ts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy changenapm)eutt v es)lc.v:j zt(hj+(8 8u 2 when you jump ael( t)c u.882js(n)azmhup+:t vtjevs high as you can?

In Fig. 6–31, water balloons are tossed from the ,) fo 2g:g7;x pfihr1je8 rxjuroof of a building, all with the same speed but with different launch angles. Which one has1jf x: ,h)xj ue8;orprf2g7ig the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above i4a+a ffe28:wsrb,dra ts lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is gi8rbw:a ra sd+a,fe2f4 ven an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m restxi gq*dja6g ) uoh0-6cs upright on a table. If you compress the spring by pressing down w0oxq i6a*- )6ghdugjc ith your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wirec8+f gm 97z:qs0)drop 4ypvp k (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball agaipq:ck p4md ys9vfr+0zo7 g)p 8nst his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top / 0+oh svmev .2dsd u/fo55evxof a waterfall falls to the pool below?deo v +0eosf5ux/5 dsvh2m.v/

Describe the energy transformations when a chil2hl8o jbt9zy0d hops around on a pogo stick.

Describe the energy transformations that take place g0l*a ejoi64qwhen a skier starts skiing down a hill, but after a time is brought to rest by sog60l i ejaq*4triking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of g 1m3kuyphu pe .hvw:hp,1i 5)height h and slides down. Does the velocity at the bottom depend on the angle of the hiy vuek 5phpg1:h,u1p.iwm3)hll if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather t(4k 3)wvolhht han stepping on top and jumping down on the other side. Explain hkv)h(o4l w3t.

Two identical arrows, oay8j*lp -- vk9hw 3rzdne with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow wv ad8ry- z3k9pjh-* lwill penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swingi)ynwmq h3g f93ng pendulum in terms of energy, (a) ignoring frictionyhg qwn3f39m ), and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater 2/a0e6qwoh6r.nk vkt than its original heightvo0 t 2er6kk6.ha /qnw? Explain.

Suppose you lift a suitcase from the floor to a table. Th wk xte ras-xawnsc9:c2094fh:sa.f ) e work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (as:hf.w94rw 2:s)s c axkfxnet9-a c0d) the weight of the suitcase?

Repeat Question 22 for th7t*4k nrc))krkafzm*vd1rzde 6e.5 we power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb strx+pbe4 t m4kk1;p+oduaight up? m bt+ou1+; kkdx4ppe4

Recall from Chapter 4, Example 4–14, that you can use a pulley and roplmms 9m+ zn0 5r87:2ekvgglzxes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for everys:l5z0vze8 2 lk rmm9mgg+7xn meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitatixjsf7e/-fgc97zg : q3 mg8a lhonal force when a 265-kg pile driver falls7hgx z8a- ce/:gqjslf9 fm7 g3 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m hig fco g0hrd6n/0gjgvn+cq96+ hh. How much work is required? h0vn9+6f 60hng+ jcg og/drqc   J

  A 1300-N crate rests on the floor. How muchs/publq) e42u work is required to move it at constant speed (a) 4.0 m along the flpulbq /)4 us2eoor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a y:i8s bh6uk(e4z cek3160-kg crate 10.3 m across a rough floor withec3ib 84(hzu6 eyks k:out acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force acro+ram1xc/q*u9 0h9g kxhlaql)r(us4 hss a floor at a rate of for 7.0 s. Find the nex *ura h1( ukq9hxcr0+lslgmq /)4ah9t work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1 o1dyhea).4 mw;y 8k pz5xc5od.7 kg, lie flat on a table. How much work is required to stack them one8ahm p d4 )z5oxw odyc.ke5;1y on top of another?    J

A lever such as that shown in Fig. 6-35 can be used toly3io t3a-c 0z liff objects we might not otherwise be able to liff. Show that the ratio of output forceci-a3 o3z 0tly, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline andtez 7ol-3/k2-gvj rst3 n6xhdp9v ii2 is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). Thk 7v2x/vg 26 jtl3-rpeoz ihi-sdtn3 9e effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an acceler98-f (znb m vzhwgs.2xdm 1j/pation of 0.10 g upwardgj / z-vpf sxdhwzb(1.8nm2m9 .    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is ap tts,2wy (wef+,8ob iah4 0klinear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the6g td,7u1 ;tz ,iufqctf8 nkc ti28/zi x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m uzt8/q71it, cci i2tugf6dtk8fn;, zto x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted o5 9,b7qfah xvvn a particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen r/ju mb0 8jv6kmolecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speed inci56ah:-n -gc7svco gg reased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electr::kwjni 9fd+i djb7me og4izz3:gi2 1on $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to st8g+m fqu,x t6oop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average :yb1o xx nx(1yforce of 110 N on the arrow over a distance of 78 cm. What is the speed oxxo1n( x yb1y:f the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s o) -lg lmm7e(lyk j+ )px9xat5moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on thej-m+)agllp7e 5k l(x9 t)om yx glove?    N

If the speed of a car is incrcudkl ofm;, 31eased by 50%, by what factor will its minimum braki3 1cko lm,udf;ng distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scenev + t /p yvliz3r+lbdio:p4o4; on a level road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Ul:vi4/+3otiblz+ dvp4py r; ose these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reaches s0/.p/rt+xwm uy zz cf.(k+f cthe plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the dis.c++yzufpctm s(. x fr0/zkw/tance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown stra7eg fogujq 3,zi6 h;;eight up by someone who does 80.0 J of work on it? Neglect air resefi, g6zg;o7 q u;3ehjistance.    m

  A 285-kg load is lifted 22.0 m vertically with an ac:at,07r+rf6l i wtpsfly h )rv,a95enceleration by a single cable. Determl :wa6ra,tlef7r+ pyr h95 snf)i0,tvine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must thi73hqyy -pqh+g*- ox7t)gc kaf s spring be stretched to store 25 J of potentocx kfg7ghqhyyp- 73q- *t)+aial energy?    m

  A 7.0-kg monkey swings z.rh,r0v13j3eyr9 ct 3 nyczs from one branch to another 1.2 m higher. What is the change in3ye v z3ccrrzt13y sj,0r9nh. potential energy?    J

  By how much does the gravitational potential energy of ahmt. k8iwv16too:/tz 64-kg pole vaulter change if his centt6 kmovt: .1z8hiw/ oter of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface e.7b2ysk; a uwm-q;o;ou1k tyz, duj/d7n rr6 has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2y;ne/dut1ry 6ub zoka-ko ;w sj7m,27q;d.ur m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m auhyr6fr2),dn 0el*wd bove the ground. What is the potential energy of the bo0l2*,rdd 6w)yru hfneok relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to th beg k0 :xe/eu izxhof44kf1oa4k )g3*e top of a 3300-m p/4a h)*fz oexe4fx u43kg 1gk0:koebieak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically n+-ewiw jkzg yv i+vr /3v:h*o)ext to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to*h )v/ ev3-r: kwiozwi +yjg+v the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/k/r l/ns-kr;jz+0vska zj/4 eprt 5+bs) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upwar;r/4jkr+lskr/easp- /0+ kj5tvbnz z d?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slideru4 bkeem dxzy,6raq,(-e f/ w-t, qg:s down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a fricti:6 x +q.l/2zjrq hr9jkb5(y+1px wyxi ys /hxhonless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinex5q pb (z 5*f5kecd3drtic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar wix k d qfpdr535*5(cbezth a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertical+6i)v57 tuc:ici qvp:g6g . bh4rcwdxly upward from the top of a platform with a gcr6i).7pt:+4vdvw gqcub ix6:i5 hcspeed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring stiffness constant is 950w/u/0c; -p rnpg: s9idymo e(zN/m is attached to a table and p9 /yns g(wr:-po0eczu;im /dis compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without frictionc.:zznjpy,n, /vc b q-a )(gyf along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose cqa(fp ,z,.gncj n)yz y b-:v/radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of2dglm 1q1h wj: a spring (spring stiffness constant k)2hgm jqw: 1d1l, Fig. 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied 6he1lmob4 u a7to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming 4l6bueoh1a m7 Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 whevdi-h hmp 537znf6p/ jre it is released from rest. Assuming n-5idmp/ fhv7hzp36 jno friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a fr3xqfuq150g speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an eledzibqy i;/ q8f,g). bovator shaft. If the elevator cable should break when the elevator isi,z.biq;dq)oyf/ g8 b at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up h+fz+jgwrvi-g g,c1 7p 29rff a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7uy , tqxhcf 58g0rd3p27pqs. i650 kg and traveling 95km/h in opposite directions, collide 0.8,p2 3ch sr xtq 57udfipqgyhead-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high atf )ozo qhk(8i.fy86e(*6 fadlauw q7nd reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction washt 78l u8eyf)*q ( iqf(a6.dokofwaz6 generated in this process?    J

  A ski starts from rest and slides dowbnkx:aoxob 7,d, n5, kn a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped fdn3qln/- lj4dob7v .arom a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and itht h0ohuyp+4 6 bounces back to a height of 1.5 m hthpo4u0h6+y .
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled acro3jhxoscd -ln7p)b e0 +ss a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionles0c3 n7 -lhxobp e)js+ds, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41hp2 ,+vvpz 3fv b 5,vk9udjphj-+u5ko passes point 1 with a speed of If the average force of friction is equal to onh25du3pj ,vkvpk++9puhv- v of,zb j5e-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward w8zs p1b67gkf 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attacedk580tf jdnw r/)2re hed to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibr/ree 5df jdrt)nk802wium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly atta ic */gf:f90k:zjjwim ched to a very light horizontal spring, Fig. 6–40. The blo/*k wcim:z fj 0ig:fj9ck can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg is ywi.1w*te8totp bsub8 +;4pncluding pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventua8ip4teb .tu+*w1owsp;8t sbylly landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a 9 .puhi twjv (65;)6mwbszjxu sixth-story window 16.0 m above? vuhij;s.9)jm(5t6 6w pwuzx b   s

  If a car generates 1q:rt chi7px)4k agq308 hp when traveling at a steady 88km/h what must be the average force cx0irh4:t ) 3kg7aqpq exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to ;yvbd ;i0sak 9n .o/n1ld h9+ dwr;jtn95km/h in 7.4 s. What is the average pd9/;ay sbr9dh 1v nt w.n;k ;j+0iodlnower delivered by the engine?$\approx$    hp

  (a) Show that one Brde5-xltoxc0u 02t5l a 0g-nskitish horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of z70zu iyhg d+dy 8iv :rn2ik63“kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in abiez jb.ksq: ,1pk(y ;oout 6.0 s on the level wh .,ky ;b :izsjoe(p1qken it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 higg7 0*a d*vrr? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion takuuv6 lszv3ht+bnow5p,e(4e3es 1.5 s, what average power wa6,uvop4l 3 uv (zenhwb3+ 5sets developed?$\approx$    W

  A pump is to lift 18.0 kg of wjkxj**4 rdu ez:fb5 z q*35htvbv g-g-ater per minute through a height of 3.60 m. What output rating (*4-fb: z *be jvgjx u-dzrvqt h5g*k53watts) should the pump motor have?    W

  During a workout, the b, y n-bicyu4.emu+xg2vp+/mfootball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 v2/. yu 4u+mc+b-by ,xm pgeinm long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclistr3.g:almnk.ge weo2x5.xt i 1 climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 19psimvea1.20/ e fd9qf hwfv320 hp. How steep a hill can it climb at a constant speed of 75km/h if the e p2eh9 9/msf 3fqvi0.dvfwa 1frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box along )syrdqt ,h hx+ o6ri*ado,ft,ntt15 2a level floor at a speed of 1.2m/s if d1 qhid+,)yxsth2a ort, *nt5rt, fo6the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7ch) bsw3,k si,.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that are des 6ryohxc+b/0bigned to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assumingrb /b+c6x0oy h the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.n1ecbm 0o v0 gq2om6i-q;/v*bv rb .gq0 cm off the ground, and the remaining four shelves are .inv q0mbov r bq6 *0 ;qv21/mobgg-eceach spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–420/b8c.e vk w vg.6i v3erq(kcb) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of 6k cv q3vi.krc/0g.we e8b (vbthe arc?   m/s

  The block of mass m sliding without friction along thv5k aglp,fy 4g )h+/xk c84pnxe looped track shown in Fig. 6–39 is to remayvp+ c/8f )kx g,h4glak54xnpin on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his par ;do7jjjmzmc,ub9 uy)t:p(iii * ;4y dachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the piloiu)9,7 my ;:by jmuodt4cj;zjiidp (*t’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is fix6zu5ane4e8i 2 wopdy .ed (Fig. 6–43)oepd6 5a24 .w ey8nzui.
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mhs3fa1 *s9;zy81do q rjfm4mqq/9ov sountain. The climb is made in 5.0 h starting at an elevation of 2300 m.o* s m y3oz/9 fs91dq4vhq;18amfs rjq Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaksym1btl ey l(-9s2 z-sh when a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in Califo2gaozmh.yae7q(p 6nmr0 c)e 9rnia claims that its lifts can move 47,000 people per hour. If the average lift carries people about a m()a70qehgzn.e2c6p rm9yo200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the ra;ytj2r twbnv, gxvn;je5(1im)fx6b 8te of 650kg/s and falls vertically 81 m before striking the turbine blades. Calcul)j nj;b(meb ti;vgvy6xr n wfx8,1t52ate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical rd9blnq 3hxxh9+,9nrr2t yk 5loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on +b9t,9nnky r5drl39rqh x2xhthe size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a can4 *g ) nzro yd)8gpx:/irgk+zsdy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=o:8rk snp*/+ z gyid4r)x )zgg1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angls1s ke.m o3y )zxcvns1ke/(, 1kmfy(ae of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, tw;sigi. ap u,8he spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, s;.,i pgiauw 8what does the scale read at its peak?    N

  A 65-kg student runs aepr3by ()wd e ygo-62w*y/v86svdhunt 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases th6g-6db*s )yo vned/uy pwrvhy(we 328 e rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m im8 /,gymf:gnwlxu ::w o4t3vq n 9.0 s. What minimum power output was used to accompygw: 8 :un3xgm fqm/, towl:4vlish this feat?    W

  Some electric-power companies use water to store energy. Waig2q klt w3*czpw;4(/vp sqp7 ter is pumped by reversible turbvz24 w;p wc/ppt*sq7i3gkl q(ine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cutr8fd crt892ra in half. What is the spring stiffness constant for eachrrf9da2r 8 tc8 of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up 1r jh-8x05 nxad/7xbqudh:. ghlb7yw a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can acc::kfb 5jj5eyggqpp3/ elerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictiona g p3 y5eg5pkb:/jqj:fl losses.    s

  In a common test forn 5hjt2 9t8 (cpo0mkr*rtwk (w cardiac function (the “stress test”), the patient walks on an in wh wt(r*r2 j9(m0k okt58ctpnclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a dist3fo6 -ewqan4to n(z myyg +2m78ol1v oance of 500 m, what was itm-tye y3ow (g o74 q n1o+8azlfo6vn2ms velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s (a7 bjdnj3u:o) h) If this water wheel is set up to provide electricity outh3bno:u7 )j djput, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s