In what ways is the word “work” as used in eve m5a:l 2q011jhbhecv ke1 npvug1g(*i ryday language the same as that defiph5q l11:v0*uime h21( b1jgvkecna gned in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an obj 1*kqwtfvlnt.z43 :j 9; p9 vtkvnxoa2ect? Explain.

Can the normal force on ancuwgu.6 p1p/z object ever do work? Explain.

A woman swimming upstream is not moving with rek1ig.3d 2nyosspect to the shore. Is she doing any work? If she stops swimmingn1i2d.yso3 kg and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider whasm)8 vzkkb jny,- vl: phz24(lt happens to the dish:l vjz8m)(, knshp24kbzvl-yes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are dog. o(4knqme (ning no worko g.qke mn(n4(?

You have two springs that aex 4( /td1;tt,eiz r1n pk/yisre identical except that spring l is stiffer than spring t ie idyt/4x,;tn (11ek/s rzp2 $(k_1>k_2).$ 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 ; v v:t;;0gddvlhda,j ,5acpb 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 hasa0hldct:g;;5 adb ;,v jdpv, v 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 change when y+z wjq;/vxg3/lz of uxbu4sz-7v z,(fou jump as higw x/( 7q/fvuzbg uzxz;3j v4l- o,z+fsh as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building n x-(:)mjq5) yg( kkkflqtkm(, all with the same speed but with different launch angles. Which one has the highgnxk)((j -kk(ymq5 )mk l: ftqest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowdo8x95p 7 syhpest point in two different ways (Fig. 6–32). During both launch px7d5hys 89opes, 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 springmj+ 4uegtvxx7x 5 ),lf by pressing down with y7+xxx5l)mj et 4guf, vour hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel ,qs;uexgw z6/wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball again/ , uqgxzew;s6st 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 axzz; 79t zox8r waterfall fa8xxzt9;7 oz rzlls to the pool below?

Describe the energy transfogn 4e3nh 63dbarmations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts p:gwvxzm rf 2n*(lfvv7k,x1( rw4x,o skiing down a hill, but after a time is brought to rest by st gvl k,moxnf7 ,:4vzww*2 x(1fp(vrx rriking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of:mc j x,bmd1/k height h and slides down. Does the velocity at the bottom depend on the angle of1,m/cxj k: dbm 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 their path rather than stewp9kds +d79nkhq a0(4 7 ainpspping on top and jumping dowaq 0n77h (adssik9 dk pw+4np9n on the other side. Explain.

Two identical arrows, one with tkx)tju :hzzh- p p;-b0wice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, thek zh b-;hpzp )0:u-xjt faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in ter1o6 ao xme*dc h-2yogtb:,; sxms of energy, (a) ignoring friction, and (b) taking friction1x:ox2c om-6,tyas ;dbh*goe into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its orii +5ni(b/ zqvcgina izq(c5bi+/v nl height? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on the suuka6aevi p7als1.u3: *ix0p k+wm 1noitcase dependaonk x7.kpis:pma*u 31+1wu l e60ivas on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the1-ek: kdh:afh work.

Why is it easier to climb a mountain via a zigzag z3 it*wo:1dls h4 mz4h,jfhizs1x c7z27p en4trail than to climb straight up?mns :4ox4 l7izizw f*hz 3z1hpjd42 st7h,c 1e

Recall from Chapter 4, Example 4–14, that you can uec 3xqs3 zp1l.se a pulley and ropes to decrease the force needed to raise a heavy l3q3z lxps1c.e oad (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force pzx3 9e)nlny6l/bz6qc6gzp5* dm/a v when a 265-kg pile driver falls 2.8zxa 3pz n6 cg nz*l9dv )y/6/65mbeplq0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.ec ls )a,w1miyh.efuo a- +/1c0 m high. How much work is rel +.,ih1 sauee c wo/cma-)y1fquired?    J

  A 1300-N crate restsuz /x9 a :.zk.ameu-utd pazsle -(8a0 on the floor. How much work is required to move it at consta txd-zl. uza.ps/z a 0u9( a8:ea-mkuent speed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg craoo nox -ilf4.-c0:h kvte 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.-lhfxkn-4 :cvoo o0i. 50?    J

  A box of mass 5.0 kg is accelerated by a force acro 3 j;0-j-7kjbmhs 4z1kzjeeja8wls( wss a floor at a rate of for 7.0 s. Find 7lj3 4e-;kkjejsswa(h j m0w 1zj8bz -the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat qef0eh3ur :vhmr) ;:p on a table. How much work is required to stack them one on top of anotheh : mhrfru3ee )0v:p;qr?    J

A lever such as that shown in Fig. 6-35 can be .4.d+cnx vjxnkx3o) ouv6 q:aused to liff objects we might not otherwise be able to liff. Show that the3njq4no. xxv)ua+ v :c .6kdxo 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 an0jl)*h*o jvb sd is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40.ovbj *l j)*0sh 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 mass8idh 1nmn(w (ht poj59 M an acceleration of 0.10 g unh(8 1oiwd(nh mtj95ppward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance 6fzal9j7d.ou71kjpsq b2,vbjf4 ,rtk 5.c i faxis 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 Fig. k-y 17:ylqk2ec3qx eb6–37. Determine the work done by th1ybxe27clyqe:k 3-qkis 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 y(;d6cqdx h .oparticle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen movhsa0mx-a1/y k. sl-q lecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has io+ic(c5kj;czg, d+isvgcv . 5ts speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an el6eztwc 7,x w7cectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 atv: x7dzb8:ktm 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average fo zyig*l ulu ng 1l/h+/v/f(dd,xfa70zrce of 110 N on the arrow over a distance of 78 cm. What i i/h/uagdldvf *7ux,+z y0 n(l fz1/gls the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) trav mt71h3knwa 7veling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was thek tmn7wa317h v average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by hfzack q8f99zbp5 .5* a)kqlhwhat factor will its minimum braking distance be increased, assuming all else is the same? Igp 5fhb9lzf5k)q*qzkah 89 c .anore the driver’s reaction time.

  At an accident scene on a level ru) 0nqtr0) jeecn z4)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.z)q )nrc)ertun0e0 j 442. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pihp7)q os;ud,(x+ynl btched at By the time it reaches the plate, it may have slowed by 10%. Nnsd)b7xqo(u , h;p+ lyeglecting 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-kgh q kmixp)lmu7gg;6, 0)2dtgs rock go if thrown straight up by someone who does 80.0 J of work6m 0hu) 7g ,lg2;piq dgmsxt)k on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m verss 7bx,(ik9ik 3iep6rtically with an acceleration by a single cable. Deterpisbk e376(s ik xr9i,mine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must this yy:, xds1 rm+;e qfchp g8ik953o:onmspring be stretched to store 25 J of potential energyymi1 h3ks8qdgep;xr9 mco o f:y5,:n+?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What i wf95f;x yovs9s the change 9vwfy95xo ;sfin potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vault se+41oq*utmg )3ushqer change if his center of mass rises about 4.0 m during the jue)1qho +uq uts4*m3s gmp?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 6,c1kvv2 xvezy94m ;fd5 km/h when it strikes a horizontal coiled spring and is brought to rest inv12xm ;dzfk4c y, ve9v 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 it is 2.20 ms h5l7m4f o4j7he6tydyp/,cgcc* b +d above the g7co4+fyh 7b*54j gyspd/lct hecd,6mround. 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 elevati;p1i ix-yq p)7 1czkjeon of 1600 m and climbs to the top of a 3300-m peak.x1 p;y) -zici17ejk pq
(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 the springpvwenlbj 7+w;) d.mj)vq ;bt0 is next tnw 7dm+jb b.)t;)vpvw; ql e0jo the 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 (5.3wgx,ae/ ;,e diu-0ogma a3hy:m/s) and grabs a vine hanging vertically from aoe:0g i, h,/am;3gduaye xw-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 fo:i5ueuk.vl,6l (al xrom 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 frjh aj ug8mp(jzqj;u l:8, bq,.ictionless 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 transformea 1.emypqe1-t d into gravitational potential energy without the aid of a pole. With what typq1am-1 e.eminimum 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.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platform wit l9vfdjscn0*;ff3lf+ lo3 .ozwtn1 d*h a speed olddjo*f9clow3tf0+vl f ;n szf .n *13f 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 mass4 92hwfqk z5khbl. ip)), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwaz42q5fw p.hb)k klih9rd 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 with5y1 3nahp) thrpy ay);eqh6g8v g.y t-out friction along the looped track shown in Fig. 6–39. If the block .;vyhg)np-3)15 y6 eh ytratphgy8 qais to remain 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 the end of a sproe5v ,l7e4 kasing (spring stiffness constant k), Fig. 6–40. The block ieoksav l 57e,4s 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 cord whose un+rs( zkrh+ln5tv/-vv wns a f 2v64+axstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffnv/wn x r(++2hfztk4s6an-vvr5 va s+less 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 qnow;zs5- 6efxuq;9 6rsjf j25m;cg ein Fig. 6–41 is dragged up to point 1 where it is released from restfee2q6jf ;n;j -s ;9so5guz xrmw6cq 5. 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 speed of 12 m/.o+y nzi0 2qyws 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 a8- dfszqfw.-o1zg.idv in/ c- 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 thef c-g/-f-z1n zq w.sodi8 dvi. 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 nncxtq:3ncx93w ;cf2up 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 76b +of:fmme3; ,cuwc- s50 kg and traveling 95km/h in opposite directions, collide -f e 3+:;mccfums b,wohead-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 bottom wpc8t x0 sre7+mith a speed of 2.20s+x mt8r 7cpem/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides o raysz);pi,; 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 above the ground,wc pq j*ut di54h/x:l.
(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 2dk(5s j:,yr*jh1sm ah.0 m, and it bounces back to a height of 1.5 msm1d,*rjja 5hs h: (ky.
(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 tko1/ k-iu(va. h(byt floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, anvhk1o .i /t y-(t(abukd 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 point 1 with a speedr1u 1bgq72w,c(us 6v +ujrje v of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach poinrug7 ,ru2q 6ejvcs+ 11vbj (uwt 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the f( ogk- b/fg nslnvq8n 9e0zc5j90uk1foot 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*gbc -2u i5wc rs;zbx*anot4 8 a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the b4unbxgs8z ;o-icawr c5 2* t*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 coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very aceg m.w+iur38bko9b z 9j5ykgr 4*;nlight horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30eo9rbu9 zmra+3y g*c k.;n4bjgw k i58. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg includi *9;sfvjh+ixa ng pilot) that was launched horizontally at 500km/h frox i sj;*+fhav9m a height of 3500 m. The glider eventually 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 sixth-sthqxa xs8 s.ywg( ;v*8+ foku4xory windosuy .w( 4kv+oh *sgaxf8q;x8xw 16.0 m above?    s

  If a car generates 18 hp when traveling at a o ss :/ /so+v/f1peaqqe,( ikssteady 88km/h what must be the average force exerted on the car due to friction and o se(s// e ak1fvo:s+p/s, qiqair resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the a:ywo*bq7 8j cvveragw 7byv :qj*co8e power delivered by the engine?$\approx$    hp

  (a) Show that one British hor/(de ir:tgsplf1r : *isepower$ \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 theto,,k dsouuy, .bhd998;bnww 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 that her 1150-kg car slows down from to 6 w qr2 pj3btebam0+.im2n .dmbmcjs:-/3 jol55km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is 2t - bj3.sjd 3pmi.5lbmnmb: qaco0j/me+2wr needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a xew/j o u**,nn ;3+dams -sots8scjw 13.0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motiontao38w c..ll htd1 ux* takes 1.5 s, what average poww 3.tu8taolc* d1lxh.er was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per min pu */ywgw5sr pl5w- q4wvd;peb;(r(cute through a height of 3.60 m. What output rating (watts) should the(5 pg/b; rq4vywww;srd(eplu- cp* 5w pump motor have?    W

  During a workout, the football players at State U. ran up the stadium staiu69d 9rius:vwc*:yvd* 0z cjtrs in 66 s. The stairs are 140 m long and inclined at an angle of 3zj0dyv r6cuc:i9utw sd:* *9v2 $^{\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 sjs;3k3y4qaoini o13t8 . v0pilkf /ha 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 hilldlj -;nup 13mj can it climb at a constant speed of 75km/h if the frictional fo- ;nlj dju1p3mrces add up to 650 N?    $^{\circ} $

  What minimum horsepower 0ei obvs4cc(xl1/5 dy)lj5y7q6tef s must a motor have to be able to drag a 310-kg box along a level floor aty jc/ly5v5bdfi o(q1cs)el7e4x 0 6s t a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down ,iadt l5,3m vrqzv-/ 8cujh4dx :w8fya 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 yupv a8a46cx+ u. j6xd93 r zeduny(n7are designed to compress and rebound elastically without any physical damag vuxuy6p 8yej 6 na(n3du9d7+r xc4z.ae 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 ground, and the re9ohdtinx r6hl2c5.f 5jro+5y maining 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, assuming the books are all laying flat on the floor .j5 5hto6cn + dy9r2hx5oirlfto start? $\approx$    J

  A film of Jesse Owens’s famous lon(f) /lmnwujp0y:m3ls g jump (Fig. 6–42) 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 spee3(:suyjl/ m fpml )w0nd 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 witho+6s rxhszn3, out friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top rx, s6znh+s 3oof 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 wi oc2+)glzmlo* thout his parachute opening. He landed in a snowbank, creating a crater 1.1 2 +l o*l)zgcomm deep, but 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 horizontal cord of length L whose other ennow2 (kc8 a/kbd is fixed (Fig. 6n( w/co 82bkka–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 climbxf*hme /et an 5s:t(a: is made in 5.0 h startin( /5aeftmnx:*:she at g 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 aboved/ 6)athalibsgc *a 38 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 claims that its lifts capg7j b+;pe 4jjn move 47,000 people per hour. If the average lifgjbp 4+ jpje7;t carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at ts/ o 1mb;qnn1-m ym2tvhe rate of 650kg/s and falls vertically 81 m before strikingt;m 2y1-m mn1 /bvsqon 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 a cok7dl(6q-bn q ircular 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 a 67qqn-lbod( kbove 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 nxm .t22 xaiz+high could an 82-kg man climb a ladder if he were 2tx .ia+n m2zxfueled 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 aoj dbg7t,0uw/tp ,.szn 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 sca6.ma6; t2 ygqvyxefs3le, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from6exsy2amy.3 vt; 6fg q 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, 1)wnv4b hl0 d jgr4bsujjm*-td ,q19n and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zerodj4)1q,sd mhwjb-r 4 g*vjlt 0bn9n1u.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m dkx2x7kblp qj2 u m+ v7t-z1h7in 9.0 s. What minimum power output was kh77 l2dtx1kbmqx-pzv7 2 +uj used to accomplish this feat?    W

  Some electric-power companies use water to iqsxd3x i7e56store energy. Water is pumped by reversible turbine pumps from a low to a high x6iqesx7d35 ireservoir. 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 spring sti x2ilr4+h f6dji c cn6:1zgt7cd)h *siffness constant for *6ign:x cd rfc1s hzt d ihi4j7l)c26+each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37 z w-pb9 zn:,vmjv/md($^{\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 ; mcitxfvrfnn:*8/: w long will it take to accelerate from 55km/h to 75km/h Assume thffm:iwn n /: c;tr8*xve power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the pahgwza, )f4osm;ck0p(s(pg qljm k933 tient walks on an inclined treadmill (Fig. 6–46). Estimgpqog;(msks93j w3zc k(a)m 4 l,f p0hate 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) c)3tb0 up06z8u 0kuaqkpjz2(osq 9kxs :p xc a distance of 500 m, what was its velocitk0zpup:b szu 90kj)p3 2(s ) 6qu q0xt8xocckay when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s (a) Ifx zic :.3ceouddhp5-e)0e dh( this water wheel edh z xche:p3dou -0.e(dci5) is set up 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