In what ways is the word “wot/9fhej.il9 gt4t c t*z5l,wo rk” as used in everyday language the same as that defined in physics? cli. 4e5t/g*tf9tl, t zj9h woIn what ways is it different? Give examples of both.

Can a centripetal force ever do work on an objyfwq*ns)qcpu k p;z.:2we+bm3(r3py ect? Explain.

Can the normal forceneck: yq vc ;722-xgho on an object ever do work? Explain.

A woman swimming upstream is not moving with ref1/jg ( 1dvm4gpewqz5 spect to the shore. Is she doing any work? If shefp v/1 gmzedq (g5j1w4 stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider w3aqtczo;8 0 :-qhszuxhat happens to the zz 0x-:as;qh83 otqc udishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even dbg/w (rwmw- 8though you are doing no wormbw/8 -wd gwr(k?

You have two springs that are identical except that sprqxcz( c.nc.b7 ing l is stiffer than springcx b7qc .nz.(c 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 horizontalyqdidjy4; zfl+ k+e :3 force on a block that is free 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 dista : 4f; kyjd3qzeliy+d+nce $d$ 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 ml7et4r4w b9 lp/w cj8xvg,a0tuch does your gravitational potential energy change when you jump as high as you cana8w4pte74jc vl xbtg,lr/0w9 ?

In Fig. 6–31, water balloons are tossed f.mw(fr qb ohuff:g8bwv952z kd(+8rfrom the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on g dbk+f(9rfzfo5.: w(fh mqu2r 8 b8wvimpact? Ignore air resistance.

A pendulum is launched from a point that is a h x4hb2yvp1cn3eight h above its lowest point in two different ways (Fig. 6–3123hvyp c4nbx 2). 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. 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 table. If you compress the spring b kms7r*.gl*x2(kgrsay( (skhy pressing down with your hand and then release it, can the spring leave the table? Explain, using thmr(g7sha .gkr* (l kx(2s*yske law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 152vvnmk n/85 zpdaph6–33). The instructor pulls the ball back and stands against the wall with the ball against his 51v5h mv8p npk zna2/dnose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energtk)2ecw4j( wd y when water at the top of a waterfall falls to the poole wj2 4wc)(ktd below?

Describe the energy transformatioo242lvjpt -guns when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier star:,pguwbjan dro sg )j,ok ft p8/r0429ts skiing down a hill, but after a time is brought to rest by striking a snow j ong49gftpjk ) ,8drrwbu2 :osa,p0/drift.

A child on a sled (th y581 stgfqi8otal mass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (tisgq5 8 18fyha) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen logn4ga-p m2wz 7+v ;6fa.qha qwn in their path rather than stepping on top and jumf; aapa-q64whgn+ w 7z2nqv. mping down on the other side. Explain.

Two identical arrows, one with twice the speed of the o3(;keuqh b/tl*a d8rl ther, are fired into a bale of hay. Assuming the hay exerts a constant frictional forc/bu* e;qrhl(dt 8k3a le on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion ofkcn2b/ig) v-p tpckg9j7l9l8 -gb r/w a simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking fri9kclipgrp j/8-)wbtg bgn k-2c7l9 /vction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height gr/kfoj )zf0b (i*3ysrh eater than its original hsff*bkr0oy i)j(zh /3eight? Explain.

Suppose you lift a suitcase from tht- x0pyx7*(lffj3 uvve floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it stfv 3uxv-yp fxt7 *(j0lraight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed w h;1a7rg(jnf rather than the work.

Why is it easier to climb a mountain via a zigzag traa6:2 76yc4/mqdkbp m aup (cj)tzma-b il than to climb straight u6)/c: 4mmy-( ab amqtzj p2uapd6c7bkp?

Recall from Chapter 4, Example 4–14, that*vs 1g jd+ntp5 you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised,dpvtj+sg5 n*1 how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitationalfn -lnqa )w +7.naz*vc force when a 265-kg pile driver falls 2.80 m? nanv-qc +*z) 7l wanf.   J

  A 65.0-kg firefighter jkt759 38f nstea6xpfclimbs a flight of stairs 20.0 m high. How much work is requirt fn8 txes9a7j3fkp56 ed?    J

  A 1300-N crate rests on the floor. How much work is required to mo 3bk+nq5 zja (ibx/hu0ve it at constant speed (a) 4.0 m along the floor against a friction force of 230 x(05 q3n/iu+kjhbaz bN,    J
(b) 4.0 m vertically?    J

  (I) How much work did the mop -c* ,bv1pkvyra ccf0l:*4j kvers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if tp04akr ,c vvl *yp :*bcf1-kcjhe effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a flu7t srd71-9pg p ki4jorce across a floor at a rate of for 7.0 s. Find the net work done on the box.u 47tk7sgp9r lij-1 dp   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. H+:0k8nf mt xp) dnwqo6ow much worm)dn 0oq fp:6k8t xn+wk is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can o t*rwlj51t0p3kgsfst2 zq,+be used to liff objects we might not othek 3l0ow5trjz t+21ft,qg s*sprwise be able to liff. Show that 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 zn a1yia :og;n(/j+ r1 yhnu2qfrom accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient ofn(j/o 21+ay;rguiha:qznn y1 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 acceleraticg im7 (/::lv e7;qaqtewz3ektu:5f von of 0.7;mw:3f qvz(: 7etei :uegcl t qk/5av10 g upward.    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 dis4x +sxfu7j:6i wi qu3ztance 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 oo :)drf*xn*i(f sv) qalong the x axis, varies as shown in Fig. 6–37. Determine tq ff))si: ox(ron**dvhe work done 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 particle9(fvum3jp1 *tppw a,c 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 )z*pn uw3tor2 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, nh;(nzwxp(m8+ r -xgn 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 t 2f -x+up n*tu0vsk- ug;a)uojo 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 )dx t4aqqsbr(iox 7 r/7zgmer: 66 x0vtraveling 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 oa*mnf)52pe8fhmc y7 qf 110 N on the arrow over a distance of 78 cm. What is the*fmh78ecapmq n5y f2) speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling u(t c4qs.o/bo32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exer.4tq(/c osobu ted by the ball on the glove?    N

If the speed of a car is incru l*2b ed;1tyveased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the dru2e*1 t lvybd;iver’s reaction time.

  At an accident scene on a level road, investigah3)v9+vu cpc ftors 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 tvh+c93pvf) u che 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 1mbdwcekipg bh-l3 :g),y82 kBy the time it reaches the plate, ,wcm)21bpl 8eydgg : kh 3bi-kit may have slowed by 10%. Neglecting 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 wt y7ccy +a vt4z,(.ibkho does 80.0 J of work on it? Neglect air v(ty.c,ikct+ za4yb 7 resistance.    m

  A 285-kg load is lifted 22.0 m vertically with ain9( r11w q) acesbh km2vs qw/w6ad.4n acceleration by a single cable. Determin aw/6a s qm1ks(vhd.4qw92c i1nr eb)we
(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 stiffne*(mljrh jm:g s2onm2+ss constant, k, of 440N/m How much must this spring be stretched to store 25 mj(mg:+lm*o rsh2 2njJ of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m hg1btdk - jhn8/igher. What is the change in potential tkd /n 1j-bgh8energy?    J

  By how much does the gravitational potentiaww9xl5*lj y ej 4mtyt -c:(68wm1g0ti 2 nepoul energy of a 64-kg pole vaulter changmu1(lt*w2l08jm64:te95 w ytcni g-opejy w xe if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rollinjd(ka5a(+oa ig on a horizontal surface has speed v = 65 km/h when it strikes a horaok+a(jid( a5izontal 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 +c )gle+ r*;gm1zor,yhlbe 6tlifts a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relative o + 6+gmzyhebl* rr1;c)t,legto
(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 elevats-*-romkax2so0psf7 8j ikj 7ion of 1600 m and climbs to the top of a 3300-m peaix7* o sk -jsa 28f-s0mrokp7jk.
(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 ruler. The end of thek65tzof e+z3hwc/h )j0 +opcbu( ps6d spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring,o)zk u cfwo 06dtsh(+p/ 3bc5+jpehz6 where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, uy3,vw+cm ovfn 5g av )p7t(*lis running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high ca)vu( pgvav+ n wo, mt73l*f5ycn she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides downlxj+rg 6oalhhuf +h b,3a+**z 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 v go662 1dv+m6 hppes-6dqpuuup a frictionless 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 is tran v18kjfc rr )dg176xrzsformed 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 thef)g8jx1rr7 1z v crkd6 bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upigscbv q)ak5y- qkan/ n2.(- jc(dsk1ward from the top of a platform with a speed of 5.0 m/s)2jay-gn( bv ck kq n q/k5di-1(csa.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 conso.njgo0goo)p( n b) :ktant is 950N/m is attached to a table and iooknog0o: .gnbjp) ()s 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 showym+b5s;gb 9 a( fy5jbfn in Fig. 6–39. If the block is to rea +fgyb9bs;m 5(f5yb jmain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to thel,-)8u hhvv1*nlb soq4rv lw( end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initia vqn 8h -)u(14lwhvl*rovbs ,ll 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 ieix71b( xm*ec s tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) e7mx(ie*b xc1 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 Fi .hhgv*ef4sksf,( hs0g. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed at points .h *fssh4vefg 0(,shk
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a spee3j:qsi bykp- :d 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 el* x;8f7g ld b160vbzixfj*cifevator shaft. If the elevator cable should break when ;c j7dxxgbf*0l1b*6i vi ffz8the 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. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7p86m gg7: ys cr5ohb/l.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, eariol:c9)4a y vfu:a i0ch of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced incvl) 0f i :4oaaru9y:i this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a speed u /,rc a4no2igyj2ff( ayg,fcnr/ 2io2 4uj(fof 2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and sli*ng: qzo+p* d-* jthpmdes 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 av4pa . nt-n ,cwc)car)bove 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 heighiagm:s:q2 m.yps7 -ur q4z2 fdt of 2.0 m, and it bounces back to a height of 1.5 m. s2 zsq2m:gri:m.7fpa4u-y q d
(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,(b0q 4iq +(.z enqey68cw u bhw75avcf is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. Wuc5f8eqqezb7 c(b6ww iq (+v0 ha4.ynhat is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a so4)gh 22w1lnv ws oa6y c9bww)peed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled iynbs)2 ocwg64lwhw)wvo 9a2 1s 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a+ov9x agc y)l +r:6gm3.ba sx-w(eanvvg1 j5k 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 toqm( rhzgh.12t752o.y.:z sxf i t uavk a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressaox m kgiv5hq.thz1 2.:.ru7z2(yts fed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium 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 attach ieqhdc27j 4s7hche9 6ed 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 sh9heqhid26je47 c7c 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 7olpj 7,r r9bnused a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventuallp7o,b7 9rnj lry 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 sixzngbu5 kcw* o/w2x 7xmxnr7u 6c3dx.3 th-story wind .5md7gc6 u3woz3x/2xcrxx nnw7 u* bkow 16.0 m above?    s

  If a car generates 18 dgkd+-s,/x9qn4hdke) a u7uzjo9 xi 4,sg4b t hp when traveling at a steady 88km/h what must be the average force exerted on the car due to friction diex9g j-u7zs +dku4ba )ds44,q / ,htx9ongk and air resistance?    N

  A 1400-kg sports car accelerates from rest twh x5 gev:* 9zuc7mbq/o 95km/h in 7.4 s. What is the average power delivered by the enginezc vb/9x*e hgw:u7mq5?$\approx$    hp

  (a) Show that one Brit t3b4ymnucxbqi 7*c 8)ish 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 “kd5mkf3 (hy 5pdtjg1r/ ilowatt-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 ab.p li, lf4c*uuout 6.0 s on the level when it is in neutral. Approximately what power (watts a*fluulpi, 4c .nd hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do a v7k;*r+ghpp6rcg4d ao e--kin 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/n6:-y*oz8jue9u k9e qi t(smz s If this motion takes 1.5 s, s:6njiu-z z(eeu *q tkym 9o89what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water p y.6, s41g9w w7zh 2ltuo goxr+z*wuze91vqe yer minute through a height of 3.60 m. What output rv o goeyq26uywzzxtl4r, 1*z7w9 s+1hwe.9guating (watts) should the pump motor have?    W

  During a workout, the footbal4f**5kve c*5f yatwuy l players at State U. ran up the stadium stairs in 66 s. The stairs are 140 af45uc 5k* *fewvyy *tm 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 cyclt ay+gwggkl9 4v27:-ff hint 2wz)*aqist 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 120 hp. How steep a hill can it cli ;fb26wfcs-o u( jb6 ei1 h ou)q49thktd+;xfnmb at a constant speed of 75km/h if the f k -hts);wo9feh6fdt fi;n62buxq(b4 1uj +o crictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor han;u glat2+rkb2ftd3l yen -8*ve to be able to drag a 310-kg box along a +e*8 fgrat k2ltyu;dbn2-3 l nlevel floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0 /q5 yu,rbbf n4$^{\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/zu4 e2 zmg0o-bky0 gp+h(8km/h) bumpers” that are 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 t4 zp0y-e+ zgum2o0kbgested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the fij+ c x*ujsb725wiym,orst shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above tj 2 usmy,x obwj*57ci+he 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. 6–4yiaed ez902ovo7yf .4pu- eg+2) 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 ove7a90fp4oi -d. 2g uzyey+edid 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 fricf*j+ qiapi*, h5 q,btntion along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop o,qhai+ in p*t j,5*qfbf 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 3707/b mcp :p;qsh m 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 mass was 78 kg and his terminal velocity was 35m/s estimate;p7c p/sq:bh m
(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 l 79:hx 2kojzbyength L whose other end is fixed (Fi79kj2bzx :hy og. 6–43).
(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 climbxrr6;vq) esi 8 r,zj7lp8c4sa is made in 5.0 h stajvla;irces) qrx8p8 z4 r67,srting at an elevation 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 elevator is 28 m above a huge springysu, )pl.b u(c ($k=2.2\times10^{5} \mathrm{N/m}$) 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 mz4/afvvf/iwe 55sh mbe2f/7eove 47,000 people per hour. If the average lift carries people about 200 m (vertieb5 vf fzs 4h/5emi/a/ewf7v2cally) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at tf3( f1mktkpn3 he rate of 650kg/s and falls vertically 81 m before strikpt(3 fmkk1nf3 ing the 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 k e3w0sjev-qf/y..c z a circular vertical loop (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 depe 0v3kye cf qezswj-./.nd on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar dir;ok bslm/ d86d7c.ydh ectly into work, how high could an 82-kg man climb a layd bd.8mhk;lco 76 d/sdder 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 an upw0si7sv81.w uwwvhz z88c uf+m ks+p-d ard 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 compresses 0.6anauqtwt rsr,g/ l) d+u8k 4,60 mm, and it tells you your weight is 710 N. Now if you jump on the scldrtugkn8,a,t w+qar) 4 /s 6uale 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 swings out over a lake (Fig. l)v8p ;n k51u2ueayg g6–45). He relnu1y g)lue ;2kgv 8a5peases 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 j6trs nm1 -lu8n dn9,hvertical distance of 5.0 m in 9.0 s. What minimum power output wn 6jmds,891rnth u-nlas used to accomplish this feat?    W

  Some electric-power companies use water to storudmgi.l9j- a+e energy. Water is pumped by reversible turbine pumps from a l9jm+ ga du.-ilow 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 cutnjvl 3h 7o5il7bg. 0+uf3ueno in half. What is the spring stiffness constant for each of t .bo3+ulvfl i75 nh73 joe0gunhe two resulting springs?   k

  A 6.0-kg block is pushed d)/x 8wh*tca k9zvz9j 8.0 m up 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 accelerate from 35km/h to 55km/h in 3.2 s, how li51 fc1k6si-,ebqk is ong will it take to accelerate from 55km/h to 75km/h Assume the 1 1,6kesifiq -bsi5k cpower stays the same, and neglect frictional losses.    s

  In a common test for cardiac functi.apq ,eka;gn3t6gx+ c81q vlgon (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill ic gaqp,g n e.+kt1aqlx3g8; 6vs 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 disw g : xmt+ja-cr9pj40y (tuf*ytance of 500 m, what was its veloyp*-gx9 ytuj0(a m+w t4crjf:city 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)/,puv a 1m lmha6t2lpzta :n8 rate of 95kg/s (a) If this water wheel is set upa1m lzm68 h :au)a/nlpt,pt v2 to 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