In what ways is the word “work” as used in evetm4k+h kaln8znmao 3; /t dt+0n2jp v,ryday language the same as that defined in physics? In what ways is it p/n+onz+d3 k8m , nvt4mlthtkj aa;02different? Give examples of both.

Can a centripetal force zr6m)*,tt tg1,na:uk fz it.c.ct i*w ever do work on an object? Explain.

Can the normal force on an object ever dod7vhj6fkr; 3. -4moq9m sot lg work? Explain.

A woman swimming upsc0 yuco )26sg4 q,tp2lemj7 xgtream is not moving with respect to the shore. Is she doing any work? If she stops swimming and merel2tjlx) 4gm s0c2yo 6 gc,qu7epy floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint:4vyf0t70 u8zzj va-ue)7wtao Consider what happens to the dishes whe wva0uzta 7ey 4v87t 0zjf-o)un you pull a tablecloth out from under them.]

Why is it tiring to push hard agaixj ;yf6vosn7pc)8wst ;3*iy lnst a solid wall even though you are doing no w7tjs3*ol ;8;c6pxif ) vnsywyork?

You have two springs that are identical except that spring l is stiffer than sp pz/:zz//riot adsu.6 , u:gkj0yg8 htrk8g/t.z :/ dpy 0,6gjuozz:/artus hi ing 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal itm.,p/e3 zpc force on a block that is free to slide on a frictionless surface (Fig.6-30),z3tipc /pm.e. The block starts 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 cha)bcudw n9xudu*)y ;cas7i ;9nnge when you ucu)yi n) c;w*s7dn9ba 9d;u xjump as high as you can?

In Fig. 6–31, water balloons are tossen-4gds6:i1hp tbo x3 sd from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on i:6hxgt nsbs 31- 4odpimpact? Ignore air resistance.

A pendulum is launched from a poin81qg/r, h 3mqcnn*y1j st ipf(t that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initpn/ j3gfq* ns,y r mq(ich8t11ial 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 res1vh fn8y07j.kds z7ot ts upright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of t oh.zkd8 nfsj0v771 yenergy.

A bowling ball is hung from the ceiling by a steel wire (Fkjb0 ke8 i+q. a0 n)zy0row;qfig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to rel eqzfyj ko 0b8.0)0wn;riaq+kease the ball without pushing it. Why?

What happens to the gravitational potential energy l3qj m.a vfd+2when water at the top of a waterfall falls to thj.d l+3qamvf2 e pool below?

Describe the energy transformations when a child hops abh tl**p2 +hkxround on a pogo stick.

Describe the energy transformations that take p/o:lhjk2* e balace when a skier starts skiing down a hill, but after a timel:e/*jo2ha bk is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of heighzrg7qk y lki.mkifn j* y,/f,/qc06k;t 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 fr,kl kr/imqjzkgy f/0f,yc 7 .qi;kn* 6iction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to ,- osr t8* dzfsbc/om3step over a fallen log in their path rather than stepping on top and jumping down on the other side. Explain,-z t8fd*/ osbcs3o mr.

Two identical arrows, 0)r:r-ryq i xbone with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the s):y rxr-q0 birlower arrow? Explain.

Analyze the motion of a siq kq,vzy*m9n 8ob 9vx7mple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Exn*b8 7,9qmvzoky9xqv plain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height grwiw*rl2 e fn++eater than its original heiniwrew*f++l 2 ght? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on the sal9yg/2.3q7 clem fhhoc *j2l uitcase depeh9ghfl2 aelm c jc/yl.7q32*onds 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 th2qh2o e*5phl*pqsrkbe zv q,dok 69929upe,h e power needed rather than the work.

Why is it easier to climb a mountain via ahn r,/)en1q fx zigzag trail than to climb straight up?/f1 qn rn)x,he

Recall from Chapter 4, Example 5dbv7. rmdm sp )ip;0i4–14, that 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, how much rope must be pulled up? Account for this, using5 vdi mm0pibp)s.d r7; energy concepts.

  How much work is done by the gravitational force when a 265-kg pild. 01)egj2to e 7whltve driver falls72wed0egj hl1tt vo). 2.80 m?    J

  A 65.0-kg firefighter climbs a6u md/akps3+:/trodz flight of stairs 20.0 m high. How much work is required?pd/d+k6ta/3 o zsmru:    J

  A 1300-N crate rests on the floor. How much 5,sh mrt b2bo sy7)jwm3/(bsa work is required to move it at constant speed (a) 4.0 m along the floor against a fricw5bjh/3a(yr m 7m2bt,sssb ) otion force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did thk7 h1v k4zjca0oj36 ede movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of f164e z k03jok7cjavd hriction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a forcu 1rv3 o08heli a(5dixe across a floor at a rate of for 7.0 s. Find the net work done on thee13(0riadxo uh 85v il box.   J

  Eight books, each 4.3 cm thick with mass 1.7 hcmxr33dn/ 4h id3 xj(kg, lie flat on a table. How much work is required to jx(ihmnh4d/ d3rc33x stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objectzpy,oyom,-za c)0( ;boqq8ga q,r:(r 7wzhmls we might not otherwise be able to liff. Show that (,)m;p7r,br0 qaa -:o(owzy o hgqmqzl cyz,8 the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from acceleratingqe48q g0o i6aoj.mv s9 2(bfgb by a man who is pushing back on it paral io 0a(6gf9v2mqg qso84. bjeblel 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 helicopter of massv7 xxatci 3trdqp2)): e(yro ji90o8p M an acceleration of 0.10 g vx7o p c)89: 32r(qpi0ot) detryx iajupward.    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 is linear and bzkf8tcz)6-vr+ j nx ,3uf( nkthat $d_{\mathrm{A}}=10.0$ 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. 6–37. zjg),fe.xe ,/ 2fw z/yljco*wDetermine the work done by this fzjz /wfe,xf.wygej)*l o/,2c orce to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle acts i3)lt- w/tw* hn zzfp3hn 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 moleg,uyrk,*z0y45 llbzq cule, 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 its speedi yxm4h48rkna a0,ve. increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requirefh) n/du;otzbe2g l -(go.:ie d to 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-kgcx*t .d.zu6gqy ar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string er.uj3 p xnndbyo.a0m6t7t;c 8xerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow a t. pb uy3a;c. nr8j07nm6dxtos it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32x-(1tbef :, czfb*r9ffgk)+ snonpi (m/s moves a fielder’s glove backward 25 cm when the balr+- fs9 ,p):bot1fkb(zen f*gn i xc(fl is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, n(es74/n jw owp s1 (6rhm5ooyby what factor will its minimum braking distance be increased, assuminohy rj osm (7o41/ nsw6pe(nw5g all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators u6cxy u8stut) r4*kk8 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 s*k46 c )t8tru8kxu uythe 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 kgkr5yey 75 of k/a2fx.w is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air r7ea xy2w5rf o./k 5fykesistance 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 straiw(r1 m bhkhfp;xo3e 9xl.,p/bght up by someone who does 80.0 J of work o.9; xph/3l1 whb x,bekfomp(rn it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with 9 dmo9xklj.ah ra7q51a xr.; san acceleration by a single cable. Determin sl a rmh1ra.9o;xj x.a597kdqe
(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 s( 7x9p-x6y hee dv1uyztiffness constant, k, of 440N/m How much must this spring be stretched to sto1xd79h(-vzeu yx 6 ypere 25 J of potential energy?    m

  A 7.0-kg monkey swings from ofm+d 37z*n.pk 5 ywqolne branch to another 1.2 m higher. What is the change 7 5+y3lkpd f.m zw*oqnin potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter cha. rwy1pak*v 4y npth)2nge if his center of mass rises about 4.0 m during the jump? 1*p 2t ny y4rhw.apkv)   J

  A 1200-kg car rolling on a horizontal surfac1mk/z smw7+s bhtb y+3e has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to resth+z smyb7s3bw t mk1+/ 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(b04 hxl ( v*drr+6oqsa3ofls from the ground so it is 2.20 m above the grou*( h q60rx(odls43ovbraf s+lnd. 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 elevatvkjj q4s px/y 34062di )ebuiaion of 1600 m and climbs to the top of a 3300-m peak.iiyu e2abksvpqj43x0d)j/6 4
(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 en6abszx7a h y-:zfol;0d of the 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, where will the end of the spring line up with the z ;o6-xablfh 7y0:sza ruler marks?    cm

  Jane, looking for Tarzan, is running at topfp ) ec+yrq8;x/3pmr i speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upway+p;)rix meqc83f/ rprd?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionrsbz.y.vct kqz* j c)d+q3k(9 less 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionless 28n i; cbugd.gry(m i (/gi21)vp.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 transformed in4dvn t7yk0i4q39x ag eto gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/9nvdxty3 iq4g 04ek7as.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top pu3e:(ne,a-hx kgpeb75toijbe* )7 dof a platform with a speed of 5.0 m/s. :akbehxiu )3p -t7 depo7ge*,e n5 (jb($\alpha)$ 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 4lhyr2 my)is 7kjwbs 4.-g v5sspring stiffness constant is 950N/m is attached to a table and is comvl24 )h7mwj- ss5yg4 riykbs. pressed 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 ze/aifp1bg9 4without friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must 9e z pfa/ib41git be released?    r

A block of mass m is attached to the end of a spring (sp a)w o3.9( ;sds:p tf*jxxjoauring stiffness constant k), Fig. 6*du;ojx f).s wa9xa(jpts 3o: –40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bunruj8uwxyvbe+i :k/1. ml:0 f7bc e *lxgee 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 applie b1u7rw08y v:ixf*e/xb. :lum+jkc els. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 whowab 1h.f*yreg a05e. x) k-vbere it is released from rest. Assuming no friction, ce bfh)01aek5*arvgbow - yx..alculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown 8d ktpv66iaaql l8 r.*with a speed 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 placonh30veuec/dpx8bi2a nr 5: .ed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g whee a 3xd/cr. :ivon5peuhb 80n2n brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up c0o6je-+qmaj ;grk+ sa 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 travja6l c:i5tuwz4 43ioheling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this coiu3o:c4alhzwji 4t65llision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a s3u79gu dz+ vx.w aep4vpeed of 2.2m/s How much thermal energy due to friction. e 7ugwvd9pxav 34uz+ was generated in this process?    J

  A ski starts from rest and slides down a 9s 0cjf z3o2/coreujl;r,1d q22 $^{\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 drt25cf(1q7 sbcjn al :gopped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.scl. bpgrh f, nou.nj;9 4(g*lpa .n+e0 m, and it bounces back to a height of 1.5 m.u( jfb nh+4r ,pg*;ospl9n.. c lngea.
(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, b/caqa/j9 .wxt*:her 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.t :9ehbwj//r.aq* cx a30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a sg;30-hq ea6 nwxomcin8/i2zjpeed of If the average force of friction is equal to one-fifth of its weight, with what speed will 3 ih n ea/wo 80x2czi-mg;qjn6it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s yy n4zlsjcf /7-n. u*ereaches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horiztrvx 4d:d2cvmf4- *as ontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0:vvd-mfc24rd*a 4txs 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 3r o ajy/(1ivadsq*0v light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friyoar3j10da*v s/ (qviction 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 shutt so4hv 2veg/2ile used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the abhvei42/gso v2sence 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-kgj 5l e)uw;6bwi.c-bgb piano to a sixth-story windoi -w. );gjb ubwlb56cew 16.0 m above?    s

  If a car generates 18 hp when trcjy kqp 4q-m+ sfbh.c ;n+7rt1aveling at a steady 88km/h what must be the average force exerted on the car due to friction and air ;jqm ps -ht4bnrcfcq +1+yk7. resistance?    N

  A 1400-kg sports car accelerates from re58u3qijg,v e8vb5cuo f h)m i6st to 95km/h in 7.4 s. What is the average power delive8u m,f5qo63gvibve8hc i )ju 5red by the engine?$\approx$    hp

  (a) Show that one British horsep,,m868dnm n1v tcj uzaower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-hou:r8x((p dxcpwrs.”
(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 );uq)ba fie s48b *iuo20pfnocar slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed tf*o)2o4 i;8 sbiqubpn 0ea )fuo keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 7/ii0a n4mqe 9qto g twc .263syvq7oi1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 1hyj.: lz(:lfhs oi0f7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power was deve.j 0o1zhyil:lsf f( :hloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.5. vg2quqa. jz60 m. What output rating (watts) shoju..gqv52zq auld the pump motor have?    W

  During a workout, the football players at Statem k8hfnbk t/5 8*beu+y 4 rs7-,;hvo fabsceg2 U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle of 3 4hma/ n7bf kfbsrc8 kgt,;ys 2h+be 5-ev*8uo2 $^{\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 cyclisghoq3b 6pni//um vo (5t 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 c w+7)5oi- hugntwzxv7-y h y/ran it climb at a constant speed of 75km/h if the frictyourhy i7tx-)v/wg5 nw-h z 7+ional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box alonglxg g* 5q7k s//.py4gyqvx lc; a level floor at a speed of 1.2m/s *x;l//q.ky5xlc4yg pv7 qsgg if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down av 0 cc;uc/poj9 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 are;gex*:5d tr ta 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 1 5txegtar;: *d300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shz7b5hi0 zjwi 6elf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all layij z7wbi5iz60h ng flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous lonm*ewa -9paux7 g jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1am9 7exaup-w* m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in ftqb1)bg00b1 ia9zj sFig. 6–39 is to remain on the track at all times, even at the very top of the l )9baitz 10sj1qb0fbgoop 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 without his parachcg4t3jjgk i* r utu*xfzw7z *(w95as-ute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilost*4gj-z*r7wz agx3 iwk u* uf(5jt 9ct’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 ,o3kvttq)g zh:od -k/ length L whose other end is fixed (Fig. 6–43v oo)/qgt:-kt3,dzkh ).
(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 a+sodip13yvlj q/j 0. hpi (i8climb is made in 5.0 h s0hj 8v+j/. i(ay1 qslp3oiipd tarting 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 1)-mwmrxa n+ fa 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claimo 8chr1x ;gb+ps that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher,chr8 o1px;+b g estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate o;ylh6/:ap8 8 q9nhoofba5 aqsf 650kg/s and falls vertically 81 m before striking theohqypash 8la589aq/bfn6o ; : 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 circular vertical loop (Fig. 5vpb0lb.f jwu( ry8. fzv 9dtwbdy.906–44), the differey0v b tyfr.uvw8..zl90dd( 9w j 5fbbpnce in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could conv+gu8hec r n+ ci j5xsgk-;60sqert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000k +c0 -+jicqg5n8 r ;gshkxsue6J)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle 2q -xko-a.kjp 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 compressesjjpnwsg wbt8qck 4 c g5(x-g(:2 rm(j, 0.60 mm, and it tells you your weight i(n c (kjggct,pbw w48m :q2-jrj( sg5xs 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, andy q,kg+vv issq - dtw y8;ti7f*;rf:5sslpj3, swings out over a lake (Fig. 6–45). He re; 3syiqfwdrtlt8k 7+sp :ys5sf,- q*gv ijv ;,leases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 mv 76qa7 wia/ ym2ogae: in 9.0 s. What minimum power output was used to accompaomig:/ qy7 v6ew a2a7lish this feat?    W

  Some electric-power companies use wan f*tv+ p3dn6+qyzs9nter to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To storey +sqnd9t3 +pnv6fn *z 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. Whatrnwthozmsg(rgx+k:6*/ .pe m63 j 1sa is the spring stiffness constant for each of the two resulting s(z /rp6+m *m63kgw1asxr t:nhs. jeogprings?   k

  A 6.0-kg block is pushed 8.0 m up a rb avc:zqriga j8i /5)u, -cqu23e :0hnrshg.bough 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/dz0 hzpo0(jc1g t/ 7rsh in 3.2 s, how long will it take to accelerate from 55km/h to pz01/ t7cr dzhjog0 (s75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the /fb-*6dmg gsytmg)yv) lyp ++“stress test”), the patient walks on an inclined treadmill (Figm lyysf+ d) ygg *+mpg-v/6)tb. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vebofe+s8 bj:r6a47ns (2 oaguqz o5r4jrtically upward a distance of 500 m, what was its velocity when it left the volcano? b426ao5z+gano 8r f qbe(7jj 4:rsuso $\approx$    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 9gc)hn xm wm u93s22w1gu p8zd*5kg/s (a) If this water wheel is set up to provide e)hmm9 *cwd2ws gug1 x n28up3zlectricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s