In what ways is the word “work” as used in everyday language the same asm p*mlb +*j;ul;p4/ p, h(qtj/qdmjgy that defined in physics? In what/ ,/jdtqb +*4lj;;hgm uqljym*pp(mp ways is it different? Give examples of both.

Can a centripetal force ever do wt/mz030hz d4c sn /hatork on an object? Explain.

Can the normal force on a50dg(sl/cnco n object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doingt6rb-wyo5a7;9 zp8 x ebsu 0ke any work? If she stops swimming and merely flz s bb67 u0-8koey9e5twrx;ap oats, is work done on her?

Is the work done by kinetic f4h w-cjytqm ,rn/ nxlf,p74wf-7cf r(riction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out fr nf,fn7hw /-lrj-cxp yr w,qf 744ctm(om under them.]

Why is it tiring to push hard agai48i0.6m7 ijqpayr/qbedp 5ry nst a solid wall even though you are doing no w70e8rimaq/ jp qy6 ib pd5.r4york?

You have two springs that are identical except that spring l is sti34ogfiiy 7h7w ffer than spring 7wigfoh43 yi72 $(k_1>k_2).$ 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 horizo-z n: f v y,ybxubjltx**6 ai,:c9at)qntal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block lb,t 6 f* x xq,a)zuntv:iby-aj: 9*ycstarts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change wn1(h nc nbu 3.zlid :a,dj4q+ihen you jump as high as you 13 n zb,n cqn:ilua+j4dhi .(dcan?

In Fig. 6–31, water balloons are tossed from the roof of asslc3qk41-4)r:q lqj us-phtkzrk/r566 dlq building, all with the same speed but with r1rqj)3l:ql dkqss6s/r-5k kpcz6htu4 lq-4 different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above i 1pp4n cyl vb6-sj)3 *7 zjtdc+cs-oqets 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 trajectory, and on t c4-o b*6s37enc1-vzd pj )pq+yjl csthe 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 by3,z+onxg 6 u8ztckz 4y pressing down with your hand and then release it, can the spring leave the table? Explain, using thn+y,3tz 68 k u4ogczxze law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instru88lk1ffby 4xdg +9wwe37a hbs ctor pulls the ball back and stands against the wall with the ball against9g+sbh8 7ly faw1e3x8bfkdw4 his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy wh6(k 1.(eya;c:hqwa 5 vcivkwien water at the top of a waterfall fall ev:vhqci61k .k wy(aac(5wi ;s to the pool below?

Describe the energy transformations when a child hops around on:+ d(l v:b+r ;yjkthg*kjill8 a pogo stick.

Describe the energy transformations that take place whe 6mht4;9 dnq a;b6 0ayyxn/qzln a skier starts skiing down a hill, but after a time is brought to rama; zt dx9nnq/ lyq0hby ;664est by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of hee d*n9w-l 6ln.mzhyy-ight -ey n-h6zm9lywn.d*l h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log wo.xe4,1,vdwfrq ik) in their path rather than stepping on top and jumping down on thei. 4wo qwvxk,,d)rf 1e other side. Explain.

Two identical arrows, one with twice the speed of thsjd:5 ur3 u4i-kx /yaie other, are fired into a bale of hay. Assuming/sk4a du:i35xy ujri- the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion ofp;3yrg.l s gw5 a simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking frictio3g5; yp.ls gwrn into account. Explain why a grandfather clock has to be wound up.

When a “superball” is droppen.3vv7bivf:vhl zo; x j86 0mad, can it rebound to a height greater than its original height?vox3bvj8i:mn v. v 0hz6a ;7lf Explain.

Suppose you lift a suitcase from the floor to a table. The wovw 3i5zgtht u 5m2.-1c mdbfr2rk you do on the suitcase depends on which of the followingb 2gzh 5 i2u1wm 3fdrm-.tv5tc: (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 rathelj p-cu*6a;;uyhr wu0r than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb st vesr*e /71csmraight upsmcse/71*re v?

Recall from Chapter 4, Example 4–14, that you cance4uo ib36ij h31m g7)zpv -wb 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, how much rope must be pulled up? Account for ubz6i evjm7hp13bw 3- og4 )icthis, using energy concepts.

  How much work is done by the gravitational force when tdk(g1s3ndx 7f4-de zq7 ruq:a 265-kg pile driver falls 2.f1 : q7(7s eqrn-kxudt4dz3g d80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How w;9hi*bgnzz7l(l-clwo 1 a0gmuch work is requwgi wc*0 hbn; (olzz7-ll a91gired?    J

  A 1300-N crate rests on the floor. How much work a whb n-2 3k)cy9mgjk9/zq8i5u dhb )dis required to move it at constant speed (a) 4.0 m along the floor againzu8hb nw i b/jh9cy 2k )qda-3g9dm5)kst a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushi8fjk m97 tj5ukng a 160-kg crate 10.3 m across a 7m8k9tu5fjjk rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceleratl d+b tuad2ioh(bj:+ b)1 rxc*ed by a force across a floor at a rate of for 7.0 s. Find the net work done on the ab*d: r+hb( l2t x1bd+ u)ocijbox.   J

  Eight books, each 4.3 cm thick *nv*3zat rk z(v03q bowith mass 1.7 kg, lie flat on a table. How much work is required azv k(t 0*n3o b*qzr3vto stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we j(lp r*m2q bwu+wr,5e might not otherwise be able to liff. Show that the ratio of output,b r5 +mlwwr*qjpu(2e 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 ag 4fim.vc em gy/)z0: su:8uks 28° incline and is kept from accelerating by a man who 4vi u/f0s.ke:mz8u:)s c gmgy is pushing back on it parallel to 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 helicopteb(o0f 5i-r 9qb4 a/u+1wvgjpdrzsb 6sr of mass M an acceleration of 0.10 g uj5obsvwr fz (qrg4a- +9/d1s0bpib6upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis 1aqes dq* 9i4pis 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, acti (4 l7hpw 7v+pxbeh.vpng along the x axis, varies as shown in Fig. 6–37. Determi7 v+ pb4.pwh7pxlh(evne the 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 ai p)vqhy7+ ow; particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an ok8f1fi 53olfy 3f+ll zxygen 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 what factor hathwwojtqzy 1flu3 76w9k( y ;8s its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electrol,(p m e8prfp 3b2prv8n $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 vyz6 t5r xtg+egl-4,wtzn+;cat 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose s t:4 l3u2hwrjotring exerts an average force of 110 N on the arrow ove 3w: rho4j2tulr a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove bsi8izz:2ug* j ackward 25 cm when the ball is caught. What was the average force exerted by the biu* 8ijz zgs:2all on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum bra6ebwmza:u1bdo/tv 7 . king distance be increased, assuming all else is t .umbv /ta6w7do:1bze he same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid marked w1 ;qp g*h noj270dm :m3vebnp3;tt 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 slammed3;1d3h pwe 2ptm egvt njdq:b7o0m*n; 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 pvm9sx wsg ). d8ljb06gitched at By the 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 the xgs9vb)wm8 j 6d.sl0gplate and the pitcher is about 15 m.    N

  How high will a 1.85y,7zrcpbq p68rl33;l riih0j -kg rock go if thrown straight up by someone who does 80.0 J ;q bi0iy3r8rrl plhz ,c j7p63of work on it? Neglect air resistance.    m

  A 285-kg load is lifteiqq v s3ksjq:66,z 9vad 22.0 m vertically with an acceleration by a single cabli qs6:q3zvvk6j q 9,ase. Determine
(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, kzr3xb;*dnv7f :7p+rmksy 9q1 i r0rsz, of 440N/m How much must this spring be stretis*b z1rrfdxpr+m973yrk 7 :v0nzq ; sched to store 25 J of potential energy?    m

  A 7.0-kg monkey swinwa.)x ,4 v y2skutn,rngs from one branch to another 1.2 m higher. What is the change in potential energy .wnry4, ,)atn2ksv xu?    J

  By how much does the-mu34r . a i (ahcyh-uv/cb9k9w dxnb. gravitational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during cba-d-mu3cy( n4ixwhha/ ub. 9 .v kr9the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed vjfs:)-gi9 c 6cmb,j ze = 65 km/h when it strikes a horizontal coj)ec -b:mgzcsjfi9 6,iled 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 gr p4ymp1vl7h) rb+ you7ound so it is 2.20 m above the ground. What is the potential en7b) y7pulr4om vh+y1pergy 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 climbs to*bgazxrw dy5j .+ n2.j the top of a 3300-m peak. 5b nja. .dzjw2ry*x+g
(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 yyd4onggabt:l+3qv gz 4 e,/2d ;nje.spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attacho:ydg,g3nae q;gn .4 /dyv4btz+jl2eed 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 ry2v(3 3ifp0qg iz- qxeunning at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in y e3fxi-qq z3vp2(i0gthe 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 rest, sl; zhroix6k) (/yvv8x j h.j,bsides 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 frictio sx:uyndgqp( jvb57/9nless 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 h1 wpd83*jtwve.jm f(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 lip e(tf 8*wh jm3jw1.vdft 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 qe3xeum/1 ,l6lmjgg u a3(j3 nplatform with a speed of 5.0 3n3jqg xe3j/l,am(ug um6le1m/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), who1m1 preypyd144lpxy *se spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 y*4xy 14mdr1y e1 lpppm. (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 loopejo.0odol 5*i e4g+x tud track shown in Fig. 6–39. If the block is to remain o dieju0l o.g5o*ot4+xn 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 spring (spring stiffne2ntwx)x,kd /qkoghiq.a*3j -ss constant k), Fig. 6–40. The block is given an initial displacemenq,wgxiq n2h )j/ * xat.k3k-odt $x_0$ 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 fbygo hin 5+s)p fjgd+yc 354i4rom a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law as 4fj c5yygn+i5+po34) bgihdpplies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6as(v:2kf2m8 re hyi,qxu wo tn3,7q0l –41 is dragged up to point 1 where it is released from rest. A(irhxf os8q:ym2, wq7vknu3t,ale0 2 ssuming 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/s at sozcy1(( tu3 dan 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 x)vdgm /y8si*8r4x5ev:wcn1veqag 9to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k shdgm we8x :q y9ecv* 8)nxi ag/r1v45svould 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,+bvexg-/8c wn kll:j up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95kgk t g78(cxmq2:z* etum/h in opposite directions, collide head-ot8 *em u7qzkx:g( c2tgn 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/a6na* 7gpw :ga nf2hq and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this prpf6aa:2 n g/q*g7wnahocess?    J

  A ski starts from rest and w)z5pvnw4,/ krug5th b/5rg lslides 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 ef0 7pz9ig y-ntree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of 1.5qu0n;s8 hs i6x4g/f4kd5v nydd h ad35 m.g5d8fdnh4 h5d4v;3sa60 uqx/ isynd k
(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 floor with a conswddqnm ws+6/ zgjm 81 0befq3pr7q*b (tant horizontal force of 350 N. For the first 15 m the3 e7p+wr68snjq 1(b/dg bwqz0 *m qfdm floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passesolmvc r:vn/ 82 point 1 with a speed of If the average force of friction is equal to one-fifth of its we 2/l:v8 cvornmight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 18.0k 3u 9e(g *ple3o1yjcc $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very lighcmni wvve: j/)(y cev9m..-ij t horizontal spring (k=180N/m) as shown in Fig. 6–40. It is notedi-vjvjw)icnem:.. v9 (e mcy/ 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 coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal w :ogmif+,;rvop3az 3spring, Fig. 6–40. The block can slide alo3 r:ofiwav 3 pgo+z,m;ng a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 9dmp,/( jupffo4i0op8t p4 .pj80 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 speed have been in the absiot o/8 mp 4 p,j(pffdjpup.40ence 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 lglw gn*6- cns95y ;lflift a 315-kg piano to a sixth-story window 16.0 m above?*;lnf9lw gl6cng -s5y    s

  If a car generates 18 hp when travelinggfh 6i2i jo8e hqj22uf 2rfa70 at a steady 88km/h what must be the average force exerted on the car due to friction and air rfgeho2 27i08af2hj 6qu2f j iresistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7*-3/ryjvl. a tfse) vp.4 s. What is the average power delivered by the rfaystvv p-je 3.) l*/engine?$\approx$    hp

  (a) Show that one British horsi7 *u c)vi1t8el kbv3h97sesaepower$ \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 express he)3mvn-0a vred in the 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 65km/h in aboutu19xz /tq4z vxlg ux*9 qy(w/t 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is nee*z(g lutyxvxx1q9//w 9u qz4tded to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1o s ckq(8csbo)99u 2ho.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerate(sfd9h +xlu6 is a 7.3-kg shot from rest to 14m/s If this motion takes h69d+ ulxis( f1.5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through rp:5xa zf t2;ia height of 3.60 m. What output ratinf: z; rti2x5pag (watts) should the pump motor have?    W

  During a workout, the football p; (xc8l 22bux twhwr b(tz/b5ulayers at State U. ran up the stadium stairs in 66 s. The stairs auww xh x ctlrzbb82/(5(2bt;ure 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb aayhh l t *spz6l5kk6;, 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 s8*(ud ):nxquxh+ mhz of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forcem xxhs*zq:unu )( 8hd+s add up to 650 N?    $^{\circ} $

  What minimum horsepower must 1yh:9bp rlt e)rizi, 9a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the z lre9 )bpi:i ,9t1yrhcoefficient of friction is 0.45?    hp

  A bicyclist coasts do;io0obqin b1k0 5l+ll wn 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/h) bumpersvf e35gv - :0lpnkmr6b” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers pevvn03gr5kfbp : l- 6mermanently 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 8j;0amduuynymg*g qt(.3iwf .gkt n,-1-kd d 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previo0m .- mgtk;in-jn qa3 uk (8t,1d*gwgudd y.yfus 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. 6–42) in the 1936 Olympics sh5uf 0 4d0ks yxnrmkr*-ows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he nee4 rsykfx*5- dn kum0r0d at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m .,wfl oas5awu 9b 0z1qsliding without friction 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 of radius r.lbs ,w f590q.ua1zwao
(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 /s-byma fr6 yl)*) kztaircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilr-lfy)/z6*ak ts yb) mot’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 hoa)xrvq4mps/yhy2o/g vjuq i.12 :9ri rizontal cord of length L whose other end is fixed (Fig. 6–/92ov.m i4r) q/y:sq2vpiu ax1j r ygh43).
(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 g4 vrs0 fevt(;the top of a 3700-m-high mountain. The climb is made in e(f 0;vgrts 4v5.0 h starting 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 a/nigeabs5 ma,.mhno 14ge a-*bove 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 can mon l.j3u2t ;dulve 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the poj3t.ldu2l u n;wer needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81dod44zi:a5ml1m ixml9+q wm. m before striking the t+mi95i.a1l wodmqx4 4ml: dz murbine 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 verrw6o r,8u*. od(nt svqtical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the (rtw qodo8r.,* vs6n ucircular 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 ini* fyn50q*t+8cstkv sm5u9 z gto work, how high could an 82-kg man climb a ladder if he were fueled by one iuqkmt 5n zf+v g8csts5*9*0y 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 i+lw v );2kjfvupward 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 scv kgt3 p ijyvep)39;d5yz3igm/in :lcn3ek*4 ale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you ju i:;3evimj33 c3ng tg n* pylpv594iz/yke)dkmp on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings olo1l6bzmtcvsf c tln9925xp5xz 8 8 6eut over a lake (Fig. 6–45). He releases the rope wh lef1lo8ccnt9zp 5869vz bx52s mx6lten his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5. 4h1on pg;d0ke:ly2 ig0 m in 9.0 s. What minimum dley4:2 pio1ngg;h 0k power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Watern2vvd f mn::m8 is pumped by reversible turbine pumps from a lnvdm2n8: f: mvow to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is the spring /+cdl yq g/.hsdsaf-:stiffyc / :a fq/s.dl+-sdhgness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37 hq(dg dyfz3)in3b-i +uk v91fz5-xvz $^{\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 55kmk.1+; yzsawom)p e6h o/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictionah+;z.sao6m w)op e1 kyl losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks o53:0qu,iv /5dk/y lfkkmgprjn an inclined treadmill (Fig. 6–455/j yqg , pudi/mrkvfk03l:k6). 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 500j3w u6 0w o*2:h tanz+nmojm7g-kg rock vertically upward a distance of 500 m, what was its velocity when it left the volm 6 :t*onauw27g m0j jh+wnoz3cano? $\approx$    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 froo9; *f/- sbzeh/t mwpxm a height of 2.0 m at a rate of 95kg/s (a) If this e*fp hs o/9z/x-;wbmtwater wheel 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