In what ways is the word “work” as used in everyday language the same as g2a76uy* df se2rxyz -that defined in physics? In what ways is it 6-yayd2eu xg *fz7r2s different? Give examples of both.

Can a centripetal force ever do work on an object40 ps1fjz6 b9vg umn/ q,;pe0yyd owu/? Explain.

Can the normal force: ft00fz1senq q,ru. t on an object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doi4 /o5rjgauraz rn-6,ing any work? If she stops swimming and merely floatar,nou r-ra/j5i4 6gzs, is work done on her?

Is the work done by kinetic friction ;6scw1 drp uitv ta1de9c76 g.forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under thct1.usiagevp1d9 tcw; dr 766 em.]

Why is it tiring to push hard against a solid g jkd.c wn5 4-+;zrhxkwall even though you are doing no wo+ ;45kxnhd-gcj wrz. krk?

You have two springs that are +adfde,h 6:j6z l c6yfidentical except that spring l is stiffer than spring 2 66dehjcf+ 6fy:d ,l za$(k_1>k_2).$ 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 free to72hs0( 4 x:fkby gep m2azyp1y slide on a frictionless surface (Fig.6-30). The block starts from rest at þo2ezsyx:fp7 bp 1y20 amg(y4hkint 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/2bbw.v- z dae change when you jump as high as youv.a/b-z2e dw b can?

In Fig. 6–31, water balloons are tossed from the roof of 0svo:h a5ivma0 h4:isa building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance. oihv as4vm5s0ia : :0h

A pendulum is launched ffj5o27jqf8b v9yty+y;0t6 kisigdc 0 rom a point that is a height h above its lowest point 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 trajector;ybi+vqo86f kdjsf07y g tct9y0 i2 j5y, 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 rests upright on a tab/vaja:n( gjs chvh8,sg* m .n-6z ya*tle. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the v /j,n( 6aac:hstv*sya - .zg8g*jhnm law of conservation of energy.

A bowling ball is hung from the ceiling by a steel (qj+:zlq,xmzwire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushi(x: mzqqz+j,l ng it. Why?

What happens to the gravitational potentih1ako pr d2s85al energy when water at the top of a waterfall falls to the pool ap1s8d5 k rh2obelow?

Describe the energy transformations when a child8ir(srw7x klb: jj.r5 hops around on a pogo stick.

Describe the energy transformations that take pl9ac*p v qldn4/ace when a skier starts skiing down a hill, but after a time is n lqcdv*49/ap brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from0ve yrb/:tz i upkxhjm6zfi7; 6(a8/w rest at the top of a hill of height h and s:zt bi;jfakw(066xh/z78y pi r/me u vlides down. Does the velocity at the bottom depend on the angle of the hill 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 the. jj*u+nmlh *an8sgr2ir path rather than stepping on top and jumping dlrj 2gm+h *nn.sa*8ujown on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired into a bvf gt6/k ,g cs8yytb.0m1ap8 ccacdiw /w:c /5ale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster w/5bmpc,wfc.c6 //ks gv da0 gy: iayc8t18c tarrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple zebl0d(m/fgf) hhr/; swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain wh/m/gbl)ffd 0r ;e(z hhy a grandfather clock has to be wound up.

When a “superball” is dropped, hdulc)(coj9 vx/z 00y can it rebound to a height greater than its original height?ju c0 0ld) c9oz(/hyvx Explain.

Suppose you lift a suitcase from the floor to a table. Theccg+lnl0 pw j1q6d17l 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 table0jlc+ lq ln 7cp16wg1d, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than thzk8cxjuvuc6( 4 ;- d x5bs+xtbe work.

Why is it easier to climb a 6b+6 l gkkqi ksmbg84ecgqth3q.y91:mountain via a zigzag trail than to climb straight up?: .t1s 4q+ kb6 3kk6qgyiml gq9behcg8

Recall from Chapter 4, Example 4–14, that you can use a pulley and roz pf3kzq*qrb)ub j( /0pes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be prjbkz()z * 0b/qf 3puqulled up? Account for this, using energy concepts.

  How much work is done by the gravitaj1celw,(pjok* y 6bx/ tional force when a 265-kg pile driver falls 2.80ek1 j wxybp(6co/,j *l m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much wofsf8 ei-g 7- 6z2cgw9-lwujzzrk is requirzez8 lguzwwf9- -fis6c gj-27 ed?    J

  A 1300-N crate rests on the floor. How much work is required to move**1df2l 9pu2u. 2qy4ok. rhtx-,kfmcg lfno y it at constant speed (a) 4.0 m along the flnk1 mo* y,p2du-l4fgu olh2ykr f xc.2f *9t.qoor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally4u ig 0twf7oa7) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50?t4wu07f7 iaog    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a ra 5sg8m/6y mnfpte of for 7.0 s. Find the net works5 gn6m/8pfm y done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat e 1 sr0a2uy52jcnqe; afb jf m,e.+qo)on a table. How much work is required to stuj +nqy sf e; ob2 2faqa5r1ejm.)c0,eack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objectss9j p,xwo ( i;hyn4vhevabg1,ly0b ,9 we might not otherwise be able to liff. Show thpi l g(n99ev1 xj,hhv4abw y;b,0os ,yat the ratio 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 kept from acce8 d.y *g;lsccoltmu29.2jki tlerating by a man who is pushing back on it parallel tj*g89 ck 2ui s.t.2dlyl;mo cto the 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 helih zh5 ari+n2hl5e6xl (7* ddntcopter of mass M an acceleration of 0.10 g upwar7 aertzn *hld(5l hd+2 ix6n5hd.    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 disf7l,xwe7ah .ntance 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 axikx-on 4.z1cziwt .;e ks, varies as shown in Fig. 6–37. Determine the work done by this force to movko14n i;cz. xztwk. e-e 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 actsur5f; g9rx986 o()sevy ras mb 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, an9uczl ;x*ceg/txrd4g e 6l)4ao-wc( h oxygen molecule, 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 -bwemb.e* n7x 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 tff3 /80fu-9k yc nbkdto stop 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-kgcar traveling at 105 novzh0:h2 jt)k.rezc9bbn6/ km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired froqyjud0* -k h)d5oz 5 /0qpzocwm a bow whose string exerts an average force of 110 N on the arrow over a distance /qu* p5)c ozzd0hdy0j5kwqo -of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s move2y-tc8tkawms2 j ,dp*s a fielder’s glove backward 25 cm when the ball is caught. What was the average force exertt-8m 2 k days,tj*pwc2ed by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum bra- cn8p uqz-e cj3tac. 1h3gv,bking distance be increased, assuming all else is the same? Ignorecpugb zqcn18 acv.t - 3,3e-jh the driver’s reaction time.

  At an accident scene on a level road, investigators measure alm0*ca ,s7aer fuwyi4 ;v*na.p+a nq0 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 oanr,aleiam.0p7;* s+n v4u w0 y*aqfcn (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 t: k9q k e0ky el.- vnz+*wm+qwlzukf9,he time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between th9 u0 : *el wkzmvefnq-qy,+zk+.kwlk9 e plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg r4p f: pr.ve;kjd)qbfp)svw) (ock go if thrown straight up by someone who does 80.0 J of work on it? Neglect airf je:r(wpvf;kp))qdv bs 4.p) resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single wt peig7tw( ; -gb-k kh60p0bvcable. Dett ;hw k0-- p7b t0b6egvw(kpgiermine
(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 y2uckvk q5rkhk/)o) 1440N/m How much must this spring be /h k 2) qrvokkc)1k5uystretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is tqqs tx)v0o./ndkm69p gbf; 7uhe change in t0b)xf7 /smqkung;.6qvdpo 9potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole l.gm m9*l4owf;,s nd jvaulter change if his center of mass rises about .lsomjwl;f4g 9,d* nm4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speedn.jf1q 4ut8 lpvcb;wugu,m 8: v = 65 km/h when it strikes a hori1mf8jblt8 qp.uc4 u,wn;v:ugzontal coiled spring and is brought to rest in a distance of 2.2 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 i u/x8+ 0 jypm aead-4;7efeixet is 2.20 m above the ground. What is the potentiaauxd a0;7 -mfieyx4ej+ 8pe /el 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 of 1600 m and clime1kfvgi j0j*fkg.t *+s (i9pjbs to the top of a 3300-m peak. (9js.j + kgpf i*tifge*0v kj1
(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 next to a ry 37qhg*.mtjc5ku si;uler. The end of the spring is next to th3 ty;i7k.mc*u j5sqhge 15-cm mark on the 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/s) and grab96w5say -qx6rqv-itywr ;h5w 0s 8ugjs a vine hanging verwyryq-6g6u 9 5hj r5 0q-ts;8xwaivwstically 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, starting from restz znf7tae1e:xf p.2t71k(wy g, 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 frictionleb s.m 5*c(ax8uzo1hwj ss 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 kinetyxaz a:d dya9j7w 333xic 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 mas9xd:73 axwa3d zyaj3ys 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps verti1dntcx1;; u *:jyqh.wq*mf a qcally upward from the top of a platform with a speed oyqx j ;hwn*; qu11qtf*adm:.cf 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 9fy03sx0lqwp byh)tr4dw 5h1(50N/m is attached to a tablebqhftx(yys rh4 10p)w0w d53l and is 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 friction along the looped track s +ufx4 , *6nmgmtaxy8khown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), fromg+xk f6aumxym,8tn *4 what minimum height h must it be released?    r

A block of mass m is attached to the e3l ei,sjurr+s+i9q4 end of a spring (spring stiffness constant k), Fig9+rq+sr3ii,l 4ej esu. 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 to a bungee h y1emh,fco96*fu9p 1ci l a c2,xtd(qcord whose unstretched length is 12 m, and falls a total of 31 m. (a) Ca 26ffhl cp1 oy ,hucad 1e,cq9xmi9t*(lculate 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 i4 vpo2d id2(v kqo43ejn Fig. 6–41 is dragged up to point 1 where it is releao di2jd 34q(o42pk evvsed from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a sb7p-n- o4 8-h igblbjkpeed 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 e1 ss eq 1v96bhra62tqulevator 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 acceleration of no more than 5.0 g when brought to rest. Lettv b6eq91q sh6u 2r1sa M be the total mass of the elevator and passengers.

  A cyclist intends to cycocofgv n-*deok+d,g(:v q co*ko(-. oq:g t7lle 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 765r . t 6stxgkax:g81*ze0 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is .86g x1tzkt:eg* xsarproduced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the b4:0oua(22sf k as uc+f7yugc zottom with a speed of 2.2m/s How much thermal energy due + cg a2fkso7u0uf:uy2szca (4to friction was generated in this process?    J

  A ski starts from rest andou*7 x (xtu4t :d.dbdt slides 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 dropped from a tree 13.0 m abbw v/g:ipnp dcgb,*tor,, 5)jove 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 it bounces back to a height of 1.5 m zcti0o(r v6eug :rzz.o*;m0 q. z: ezr0ugq*6o tm .rzvoic (;0
(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 across a f4n;7( sgo /;kgannwxnloor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionlnsgg/wn n;o(kx a ;n47ess, 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 passes pc(ccx59 tt(bi c kvg3+oint 1 with a speed of If the 9tccgcxb(i +t3k(c v5average force of friction is equal to one-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+*mcaag )cb ww 5+v2cm 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 finp2rh7)2b7jj ay ) hy4ml hun9rmly attached 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 equilibrium position before stopping and turning back. What is the coefficiery7)y )hhja2hl4b n2pj7m nu9 nt of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fig.j y .qg20y7rjd+yk)ln 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 0k2jy+ q)7ld rn.jgyybeyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the spacv/snqtv pb:qh 1i+(9 ex)sjx.e shuttle used a “glider” (mass 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 of 200km/h (a) What would its landing p 1j9qxs+t /hnq:eb vv.s) xi(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 sazyg4b aw( p1of/gk-3ixth-story wind 4-1(kf3zgga owb/apyow 16.0 m above?    s

  If a car generates 18 hp when traveling at a( 9r ;tp9c:ac5q 1vfbclkeww* steady 88km/h what must be the average force exerted on the car due to friction and air resistance? t1fp 9rcwebkc59( *q:w;l cav   N

  A 1400-kg sports car accelerates from rest to 95km/h in lb4ro9/3v)np*d6ol3iwt j j n 7.4 s. What is the averan3wjonrpv6lol * jt9)d43b /ige power delivered by the engine?$\approx$    hp

  (a) Show that one British hox,pr d,/ ola7lrsepower$ \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 “kilowatt-hoursm1re ok/u p r:7(wy1cos,e4 oin: t9mf.”
(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 hyeszrfni tf:w 3p b+ oak (6*-(u0(efker 1150-kg car slows down from to 65km/h in about 6.0 s on the lfe+en* (kurf p(-6y0io:k3zabt(sf w evel when 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 gq/etyp dn/25ziqe1ovfj7z*p)8s* j h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14uotzir42 w-zo+43m o fm/s If this motion takes 1.5 s, what average powiou3zfoo4wm4 zt2r - +er was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a he m 1l/.*li+droejcs j.ight of 3.60 m. What output rating (watts) should the pump motor doljmi*. res1l.c/j+ have?    W

  During a workout, the football players at State U. ran up the stadium stairi3mut-j:uk qi+d a :e*s in 66 s. The stairs are 140 m longa uqi u-i*:dj mekt:3+ 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 climb r a5q8zz.kr4e 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 zb4+s lj0dj+oof 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional fos4jdbj 0 z+lo+rces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have au(q59ur lw r(to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of alru5rwuq( (9 friction is 0.45?    hp

  A bicyclist coasts dn+y-um7 uby9s;ziqbdh.a-zos h- k.*own a 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/sg)/z.s pegmli g- n*n v3j06jh) bumpers” that are designed to compress and rebound elastically witz nj*.gpgs)/6 e3-jlmgni s 0vhout 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 wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the groundm5p)6t zyywy /xcu7wm f1j07w, 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 shelf holds 25 books, how much work is required to fill all the shelves, assum)z/1jc7p y7f6wux0m mw y5tw ying 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 Olympics showeb( /.z,m6des1* fhoc kqnl/7f q(glas that his center of mass rose 1.1 mq/ l(7 zak.esom , qh/gbd6l*(cnf1fe 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 the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in Fim 61 6c.wrqz .3sqn flc8qh3tgg. 6–39 is to remain on the trac6c.m1.c gwsqqf8 hnr q36 3zltk 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 witjz+ 1u nwpuhw 10jh9y4hout his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but4 wuw+1zupj nh0j9y1h survived with only minor injuries. Assuming the pilot’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 horizontwdzjoin33:g1dfg fx8t8ye. :ksmu+ *al cord of length L whose other end is fixed (Fig. 6–43fk:.+ niod3ujxf s m8e g3:tgywd81z*).
(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 mad 6)ejr , :zz(iclgq+lwe in 5.0 h starting at an elevation of g+:6 iw,e rzcl (jl)zq2300 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 elevator is 28 m above a huge spyg f a-x6uo4m(; xqyz9ring ($k=2.2\times10^{5} \mathrm{N/m}$) 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 claims that its lifts can move 4 jxzz/7lcaob i*x.( wn-pn,j47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate thez/b z4 ljx7-,won.ip ja (*cnx power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m beff(f a18luw jca.dt(*4jq 7vpq2gd/ ulore striking the tuwu favp7lc d84(ugt(a12/dljj qqf.* rbine 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 circular vertical loop (Fa e))ox,vojg,ig. 6–44), the differenox)j,e gv,)aoce 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 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.g-0 vglaj+ 0zn4zf;qtrh 7ws 7 br2le high could an 82-kg mt0rr 4lln av z.s0;bf7gwhez+-jq 7g2an climb a ladder if he 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 a70q +unz9 l2q)by hbtsn upward angle 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 xv; v.jpn(2xl go4tyy )sb mw3 j,3wj9compresses 0.60 mm, and it tells you your weight is 7.4x vw; ypj3(sxgm3 w2vnjl t9oyj ),b10 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 runsv.sj:xkzd+i- 1bv bhmnifq . 06c0 q9z at 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He 0zdc0q m sv. fhj1-vi6:qibk9+ .bznxreleases 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 7h1lpmu1:h x9u2-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplishhm1x p1 ul:u9h this feat?    W

  Some electric-power companies use water to store energy-vs/leg0lm jke7d8p p l-eb +,. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 1ljk, 0e-/ds-7p em+vl8gepb l 20-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 stia mvspu 4s0f6;lbz,neb++co3x45 f rtffness constant k is cut in half. What is the spring stiffness constm+a4f53 ve l0cfpor b6+bt 4 zsusnx;,ant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 3 iiqs(5f sm lp6/n-fe-7 $^{\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 accelerate from p+ pw td0rm+z,lr58untw+e s;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 sa+pwpedw85 tmt;zr u +,rl n0+sme, and neglect frictional losses.    s

  In a common test for a (d:- t/f/dhic .calecardiac function (the “stress test”), the patient walks on an if :l a/-/e(dithad .ccnclined 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 verticat ek vy an+b*bb7qc;;vum21nmvw2,2 ally upward a distance of 500 m, what was its velocity when it left2v, av2utmqnkve2amcn bb;1 b;y+ 7 *w 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 fefb:,o.n ,4,l yw bcsrate of 95kg/s (a) If this water wheel is set up to provide electricity output, what s,4b fye ,: lfn.,cbwois its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s