In what ways is the word “work” as used in everyday lavw4 +kgfu2cvj0 ies)rpt ;(q1 nguage the same as that defined in physics? In what ways is it different? Give exampp2k1ur t0 v v(g s;q+4fc)eijwles of both.

Can a centripetal force ever do work on oqv (+-vt gl(xc/1ky dan object? Explain.

Can the normal force on0 *facnq go*)q an object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doingf;o -xy.ib*5mpc2g gm any work? If sh*-ybim.o25c gx ;mfpg e stops swimming and merely floats, is work done on her?

Is the work done by kinetic frictij yww mm-/c(3won forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth o (mcjw-3wmw/y ut from under them.]

Why is it tiring to ph, gux:7zf,pk00 fy-p)ggb czush hard against a solid wall even though you are doing no wor 0gkcb z0f:f-ux,)7, gyzh pgpk?

You have two springs that are identical except that spl(/ cl3jm6stobz :qh1ring l is stiffer than spril3qsl1 om6jh(:zb t/c ng 2 $(k_1>k_2).$ 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 that is u1 c/ v5nlbp x0eqd e*j;8ak2hfree to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distancl/k8 an x0v;eu5deh*pbcqj 2 1e $d$ 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 dovjia/*4m*mg, edr(ez es your gravitational potential energy change when you jump as high as you can?mz*v(g / de4*,mir eja

In Fig. 6–31, water balloons are tossed from the roof oh1.ug 9w ewf e1gizd3m1;vxqb 61nt.tf a building, all with the same speed but with differentf tvwzhgbwd3. 11nm1 qeigt;16.9exu launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest p0 bkjraar hq*dt5e3+( oint in two different ways (Fig. 6–32). During both launches, the pendulum is given 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. Wh3*( kr0j abda+rt 5eqhich launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m restsa sylou( zyuq.fvid19(5( l0y upright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Expl(ouul0 y91s yaifl.(y zqv5d( ain, using the law of conservation of energy.

A bowling ball is hung frophzn6p1r:f 1w m the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stan1hpnw: 6pf1zrds against the wall with the ball against 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 of mf1ioye5 ;hj/rkpct6 ol*y h-v-a24x a waterfall m i y6p*1-2yoovjl;t4h ax/-hck5rfe falls to the pool below?

Describe the energy transformations when a child hops around on a/,r :s p bxazp00rw,na pogo stick.

Describe the energy transfut2z0sx (,t6ax 7pxsj ormations that take place when a skier starts skiing down a hill, xuz6stj(p2, x0 as7tx but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hilld z+i1y (xa-pqvgd /7u of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is 1d/ y vz+diax u(q7p-gno friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to steps3;)gp07 e67hzzd1h 7k o -vbnnxjs ta over a fallen log in their path rather than stepping on top and jumping down on the other side. Expla o7 g 3)nn17xz jvzpshb70sha-tkd6e;in.

Two identical arrows, one with twice w5;w8 bdax wxkk40r5a3 1x vigkvda1n a,x+a2the 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 will pen0agakx1x5;d r4ak x,8di +anb w35kw12x vwv aetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) l 8*tfm/jne n4ignoring friction, and (b) taking friction into account. Explain why a gf*4/lmjnt8 enrandfather clock has to be wound up.

When a “superball” is drofm9lpnhbd)la9h+ wr3+( q ti: pped, can it rebound to a height greater than its original height? Ehph 3m+99(b :f nqiladwrtl+)xplain.

Suppose you lift a suitcase from the floor8 fau3 ;yd5dow (xitd)d. kou0 to a table. The 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 heigfo)yk;3du0xw(.d d u8o5a dtiht of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the yb)xhd92pk(h work.

Why is it easier to climb a mountain via a zigzag tra-m d7 eqkef0q0il than to climb straight up0- ke 7qmqdef0?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to dba2nxnm;fu6jb pz 26,ecrease the force needed to raise a heavy load (see Fig. 6–34). But for eve, xn;b 2a2nj z6mbpfu6ry meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is donen-g /pxb21fxkid*x y a8vx; u8 by the gravitational force when a 265-kg pile driver falls 2. 1fb/*x 8v8;2 xnaykxx-pigdu 80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m clf3gf2 j(u*iycrr01xm; h:lhigh. How much work is requi03; 1u cch*rr(2fxml:y f jglired?    J

  A 1300-N crate rests on the floor. How much work is requireb1 2llr5 jx7wpab) q8qd to move it at constant speed (a) 4.0 m along the floor against a xbp)7a8ljb 52qlwq1rfriction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crau,r4pb yz+ k-phb v84zte 10.3 m across a rough floor without acceleration, if the eff 4pu48hzkv-b yp,rzb +ective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated j 6zwb(()ym)z9j .2i fot8x(qrnv oudby a force across a floor at a rate of for 7.0 s. Find the net work done on the bo8n6mr()ty(xz2 fj)o( qb9u. iwj ozvdx.   J

  Eight books, each 4.q u;wcgs6*2x8fl; ncw m9d uz c)+xjt-3 cm thick with mass 1.7 kg, lie flat on a table. How much work is required to stack qdcwj)-slz c 8u 9w*+f;xmtn;c2gxu6them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to li fi ;ziwy mnk)f1a4(z9ff objects we might not otherwise be able to liff. Show that the ratiowa)( ;yif49finmz 1kz of output force, $F_{\mathrm{O}}$, 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 and is*6ug3 q-vz2 d hh;xviz kept from accelerating by a man who is pushing back on it parallel to tvq-h3 hdi vgz6u2z*;xhe incline (Fig. 6-36). The 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 acc ;*szvek+tw w;:0gth2ptqz,qeleration of 0.10 g z* g+z;q tqp:20ws;hke, ttw vupward.    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 t 2hn mfowle 1ss43e:+uhe distance axis is linear 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 the x axis, varies as shown in o/-apzz 9w lg7s6kf(4lm; yqt Fig. 6–37. Determine the work donep(q yftg l6a wl7 z4mzo;k9s-/ by this force to move the object (a) from x=0 m to 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 on a particle acts injxwzgbk+ ljgcb-m. ;e5; .k1 v(z(txm 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 molecule, with mass ofbx9rtx9 4/0t t nkz ,x d4mus(xul(a(d $5.31\times10^{-26}$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 t ;yys58pq72n cyk3 twdoubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to s+rop 5n. b*mx,ix5kup+ o cg3emfc7z:top an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 stop a 1250-kgcex (j4 q2fi pw.cqfla+w9bd6+ar 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 force ofuiwg;0fx07t;z+1s v u le ddk7 110 N on the arrow over af u7s;1d +eiz tlk;v0wxug d07 distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveliqma(oh.xxymvv 7u:;d0(rj;dh; xv2 hng 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was theh x0mmadohhv(2dxj ;:v; 7 r.v ;yxu(q average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what e3;ub3u l ljz(factor will its minimum braking distance be increased, abzl 3e(jl 3uu;ssuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a lekq3ksn: lmz- 0u tx,,evel 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. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. -0lseu3ktxn m,:z ,qk(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 x4x lbp 4reet-65pr sij 25+pvit reaches the plate, it may have slowed by 10%. Neglecti4t -552b+pr lrv 4pixsjpeex6ng gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who+v35csnlgw l1p; f3v i does 80.0 J of work on it? Np5gw fiv;l+sn 1c3 l3veglect air resistance.    m

  A 285-kg load is lifted 22.0 j 1yeg3;u929dhthp bs m vertically with an acceleration by a single cable. Determb91jp3h9tshe2 ; udg yine
(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 o)z8tt)lzb2 c How much must this spring be st8z)2 c b)lotztretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2085c:k qhtyqs m higher. What is the change in potential energy? q c05hqsk: ty8   J

  By how much does the gravitationa g,53j nem3xq3p ,kdzal potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m dp egakx35dz, ,jnq33m uring the jump?    J

  A 1200-kg car rolling on a horizontal surface has spe k0*e dycv+w)fed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness cons 0 e+w)*dykcvftant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground*drkdxualfu y +6)wm y0zo-9 d-y 7lb: so it is 2.20 m above the groundlkyu-0 ro7azwdd- )l y9 uyf6md: xb*+. What is the potential energy of the book 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 q7 i6axy0 4wau4 9bqi tw;z9qhj2-p gfof 1600 m and climbs to the top of a 3300-m peak.2 q-u zw4a9;w 49ga q7fyqxbh6 jiti0p
(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 verticazcnpe* y0+pb (lly next to a ruler. The end of the spring is next to the 15-cm mark on 0nyep* cz +p(bthe ruler. If a 2.5-kg mass is now attached to 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/syu*mc93f ysq9uf4/jv) /s vzq) and grabs a vine hangif) jyqvy qusumvs*3cz/9 4 /f9ng vertically from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, startings11enm*,1tz2 j2k kyo(g tfvd from rest, slides 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 frictionless 2be3x7 (yggic 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 kinetic energy 7ke qqgkfk1+ )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 with a speed of 0.7m/s.f qk1)e7kkq+g    m/s

  A 65-kg trampoline artist jumps verta qs64-x2 rdzkically upward from the top of a platform with a sp - xad2rsz6k4qeed 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 constann p y5l:v:g:u1q rf1wft is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a:p gv 5fu1nwf1lr: y:q 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 friction along the looped track s9 feu+v)jg pgdkko7 cj y,y+7/hown in Fig. 6–39. If the block is to remain on the track, even at the top oj7ky)cpj,fu+/edy 7o9gv+kg f the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the gak1 you/ 0s-rend of a spring (spring stiffness constant k), Fig. 6–40. The block is given -yk/0urg 1osaan 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 to a bungee cord wwyro-9- pp2rchose unstretched length is 12 m, and fal 29rpoyw-r -pcls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming 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 where it p uyyu)fs5j 5-z4mu;t/if ;scis released from rest. Assuming no friction, calfuj;z s; pi/futc-m uy s45y5)culate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a spexf(+;eh ;yz wsed 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 apy.1v6a)joeb vf ))y spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is 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 acceleratibo)j v)v)e.y1 y6fapa on 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 cycla83cr 7v sjesldu 32j7e up 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 7650 kg and traveling 95km/h in opposite direncz 99k sb e ii-on:4x9-saga:gp3zz7 ctions, collidzks-gb:9cei47 nnsgx :3a9p9zoi - aze head-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 and reaches the bottomfpb8 9e3uosk, tma, e, with a speed of 2.2m/s How much thermal energy due to frictia sf89ume,po bk3,t,e on was generated in this process?    J

  A ski starts from rest and slid fm62 c2u yu1uzk*dbpv*)/7hjglkxx5es down 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 droppe tio8jl vhwpk b6*xw5 u6*/r(f0fn1e vd from 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 mxp gfku) (l1i4, and it bounces back to a height of 1.5 m. 1x4k( ) pifgul
(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 pul*cq, ) lgjsta5 cu.wz:led across a floor with a constant horizontal force of 350 N. For the first at*gs5u , )q wl:.czjc15 m the floor is frictionless, 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. 6–41 pazlcx9cz.j d n(a/9 ck:sses point 1 with a speed of If the average force of friction is equal to one-fift:j /zlc9kz xd a(nc.9ch of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 129/uxh: gd.dot m/s reaches the foot of a steady upward 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 attached to a veryo(yu271h qj(6n y /xmfydilu5 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 equilibrium position before stopping and turning back. What is the coey7/u onl 2mqyfxhju1i(5 6 y(dfficient of kinetic friction between the block and the table?   

  A 280-g wood block is firml*b0 e zvu.a+an64piu ,queq* ty attached to a very light horizontal spring, Fig. 6–40. The block 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 beyoq*qiaeeu *a+uun ,v.6 b ztp04nd its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (maswk : s:lw+.ldos of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed l.w:ld: kos+wof 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 liftt /eukxt*q; )w a 315-kg piano to a sixth-story window 16.0 m ab;ttw k)e*x/qu ove?    s

  If a car generates 18 hp when traveling at a steady 88kt6 d 0*+ljlhy-kz5a urm/h what must be the average force exerted on the car due to friction and air resiklay+rd-j*t l50h uz6stance?    N

  A 1400-kg sports car accuclho0x q8a6j7/9; xtlbm,xmelerates from rest to 95km/h in 7.4 s. What is the averag79b8;06c mx ,xl qlm/uatohjxe power delivered by the engine?$\approx$    hp

  (a) Show that one Britishaft /ai 6*hendbl.29d 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 mw6,pmk -e5ai form of “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 thatuxme2-hg;jcf4 pj: i) her 1150-kg car slows down from to 65km/h in about 6.0 s on the level w ; j4egx2)i jmuc:fh-phen 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 h?yab*: 9q9horetak bjee78:o) $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg s:e ah uk/nxq.-z/9 euehot from rest to 14m/s If this motion takes 1.5 s, w/qn ux .u/9h:eea-kezhat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute throb8o 4+g9d +omjzx:lkdugh a height of 3.60 m. What output ratin 9djd :zlb kx+g4o+o8mg (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium s/ hr 3pls+gdvv9 :bmz+tairs in 66 s. The stairs a+ v +sg9p/h:r3zlmdbv re 140 m 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 cyclist cli h)5c66mhyu1md-; on:dtxtyd:k9s uumb 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 120 hp. Hta n;m 6-:wfxlqr m.rl(xe( u)ow steep a hill can it climb at a constant speed of 75km/h wx)am 6qrn xr.- tlm; (u(e:flif the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor h0;cs s/mkyqj* 2 d-civave to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of f vscydij-qc2 *;s0mk /riction is 0.45?    hp

  A bicyclist coasts down a2f,v8i m0g0z j )i 1r7(hjwo6pnhjnto 7.0 $^{\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 arck,m,-e4;tz xwmg ,de e designed 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, assuming the car has a mass of 1300 kg and is tested by ramming into a solid waegx ,tw,c4mzed, k-;mll? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, xicjorj+-7c7k0 is a*and the remaining four shelves are each 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 shea+7s*roij0 ck j7-icxlf 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. 6–42) in the 1936 Olympicg* mtg9kw:hc pbi,4ag0wt1so ;k9;s jul)my3s shows that his center of mass rose 1.1 m from launch point to the top of the abw;0 w:mt gl9koh1 j; gukgs)piy3t cmas*, 94rc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sla/n/je y1r(e biding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times/(e/ ab1jren y, 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 m256gvcb4qp/ak8km bk after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s m2c q8 5p6akmgb4 k/bkvass 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 otitlsut 10+p3q/k p wl+her end is fixed (Fig. 6ku q+3pl +p t1si/wlt0–43).
(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 mountain. The climb is made i ng ,-i*umt:3 ipzj*vin 5.0 h starting at an elevatioit n vpiz* :-mg,ij*u3n of 2300 m. 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 breaks when a 920-kg elevrg*joq1e- ex llw(p j-5p47t pator 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 California claiulekj- a;t 2i2ms that its lifts can move 47,000 people per hour. If the average lift carries people about22 i;ektljau- 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls verticalt4tcz3 re.vmb k7ve:x wk1c3 5ly 81 m before striking t4vcc3w3ke7tze1mrbx. k t:v 5he turbine blades. Calculate
(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 circulan a6ryn6oytp3 9qyi;gmiu 0+5r vertical loop (Fig. 6–44), the difference in your apparent weight at the top of triqy 6 0;o 59n63auyyn+ipmgthe 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 the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, how high 3 zbh hubp)/* hfd;,x 9tfw5zscould an 82-kg man climb a ladder if 3dhhs*, / ; btbuz9 x5)fhzpwfhe were fueled by one bar (=1000kJ)    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 angle dfab(, t jb-9 ahq)ssnj bx/y(l kk1x* d-cx)*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, the spring inside the scale compresses 3 a74qwbf)a- tzgrl7d 0.60 mm, and it te4fb l)d-3 7rqatwag z7lls you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swi2y-)u sx7p*fou7dz f f3(mw dqngs out over a lake (Fig. 6–45()ypfff2ou du* -mxsqd 7z3w7). He releases the 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 ihq*7ydh-yx :5335 krzfqdfxr vlwom77 yf1 15.0 m in 9.0 s. What minimum power output was used to accomplish this f-v5r13m r7*7yid 135fw q lqfoyhf7 xzdx:kyheat?    W

  Some electric-power companies use water to store energy. Water is pumped b pjkanu7q d3(pkf1s*/ y reversibus *1pjknqfkp(7a d/3le turbine 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 cut in half. What is the spr7rov4:c : f pw0sqbc)ming stiffness constant for each o0s:q vw)rcmop bf:c 74f the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a roug5fr 1w6e un8.zf/qw a s1hw8oth 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 acce*kcozcp9h ; 6glerate 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 neglecth*6kcpz o9gc; frictional losses.    s

  In a common test for cardiac function (the “stress*x*p vew84 fqu test”), the patient walks on an inclined trp8f xuwve *4q*eadmill (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 distance of 50cy*krel o 3o49+jgw-lro-k( p 0 m, what was its velocity when it left the vol(yc oolk+r wg* kj-49-e 3lrpocano? $\approx$    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 (a) -qz m4qliqyag )h-0nrec7(8 oIf this water wheel is set up tqi cmqr(4)z ayqen8 -0lh 7g-oo provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s