In what ways is the word “work” as used in everyday lan- jx/7wi:ucvf guage the same as that defined in iw-x cvju7f/ :physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object(z9hj b y,x6xo? Explain.

Can the normal force on an object ever do work5 a2can:0s/lpyrhi b: ? Explain.

A woman swimming upstream is not moving with respect to th.;a xmm q6-x*ap8f af2r9yodie shore. Is she doing any work? If she stops swimming and merely floats, is work done on hif6;8oarf9p * yx aq.-xmam2der?

Is the work done by kinetic friction forces always negative? [Hint: Consider h k23rev:-oa tscpd5g l*xg;r,, ( -kxv wqft,what hapq r;-tc*,hwkd -ka :lpg vx ,2 5et3sfg(orv,xpens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard aga4se/ofi p4mc;*c- dtwf k-+ nixdyh9;inst a solid wall even though you are doing no work?; *hnce-fm4ip+ id-wd9/ cso4 f tx;yk

You have two springs that are identicalh(bn fc*p(0dve 8u 90rz j0fzc except that spring l is stiffer than spring 2ehbp90z fz *8 (0(rncdv0u fjc $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to slide on 4j75phgvbux /+ ya*yoa frictionless surface (Fig.6-30). The block s gpo4a/yb* hy5xvu+ j7tarts 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 gravitlf) xjt s*:.okational potential energy change when you jump a)lo.:fx j*k tss high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building,bu(dea, dr* w6 all with the same speed but with different launch angles. Which one has the highest speed on6ub(,wr dade* impact? Ignore air resistance.

A pendulum is launched from a point that is a heigrgonwn( o+mra ;c;z(5ht h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward ac g;(nz 5rnao;o wm+r(long 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 4 3wl; e v-q)jk;j0.khhhnokyspring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of eh4 ;q.kh 0nklyj-;3vkw ej )honergy.

A bowling ball is hung from the ceiling by a ster)c, l,zh:xzy el wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball aga,:cyh )zlr,xz inst his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potcnm v /rs wa(xc1)e8onoky qp9;x. d/2ential energy when water at the top of a wac8 .ymxnad1ksro2 vc/o;) n(qw9ex /p terfall falls to the pool below?

Describe the energy transformations when a child hops around on a pogo9c./tmpr.pc eku7s* n stick.

Describe the energy transformations that take place when a tyaua(aicq+ 6bv1- all/z0haju .o6)skier starts skiing down a hill, but afterja+6av (c zha6t0-a l).1aiylb/ uouq a time is brought to rest by striking a snowdrift.

A child on a sled (total mass e5 ,fqk;1me (pv.c xdqm) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep emd(5 f1c,v ex .pq;qksnow)?

Seasoned hikers prefer to step over a fallen log in their path rather thang,cmy, k: n4tfpv(z:c stepping on top and jumping down on the other side. Explainnc( :g :,m,c zkt4yfvp.

Two identical arrows, one with twice gggd0dlasq3 eebt82 -,o7.ozthe 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 od7gz-glb 3q2t.d 8 ,oeegas0much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy 5si,od6bcdax 7i0oo3b lx 3d+, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.bo30bd l+ i5i3so 7dac xd,x6o

When a “superball” is dropped, can it rebound to a height grera-/o:uzl xpw/ge- i(ater than its origilzap :ewro g/-(ix-/ unal height? Explain.

Suppose you lift a suitcase from the floor to a table. Td2dxkius6-2 ct4kf/7 wv mme:he work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the heighu d2xk/m 62dv7w cit:k4-se fmt of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rathm3hx pbvkjx-2e4) t0ser than the work.

Why is it easier to climb a mountain via a zigosu77f xu :;ggzag trail than to climb straight up?gxgf7u o:7su;

Recall from Chapter 4, Example 4–14, that you can use a pulley and5nvs 5 yz035gk99x6 aexdbprq ropes to decrease the force needed to raise a heavy loqbpe9r v5kxs9ga5dy 5n 03 z6xad (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 theex lat-3u)r5c(pb.a h gravitational force when a 265-kg pile driver falls(l3ct)5hb. raxuae- p 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of staidhgmw1.ltz5 dq- 0)hjrs 20.0 m high. How much work is requirmtl 0qh.z)dg-51jwdh ed?    J

  A 1300-N crate rests on the floor. How much w, :m+s 8bx k dms,)riuwaq8o8qork is required to move it at constant speed (a) 4.0 m along the floor against a friction fomq o)kssmw 88uad,br:+iq,8 x rce of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 6p o1vo;hnn)a 10.3 m across a rou;pv)a16 h oonngh floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acce h:x kd:69pfsxqod9 8elerated by a force across a floor at a rate of for 7.0 s. Find the netsof8ehd:x d 6q99xp :k work done on the box.   J

  Eight books, each 4.3 cm thick with otz kt/01e4dax;pmjsn* ( qz6 mass 1.7 kg, lie flat on a table. How much work is required to stack them one on topqk4*;p xjz1t6ezsd0m/ot n (a of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we jq;; b g3qt bzems*i2o./r, krmight not otherwise be able to st3i/z k*jr;b,q;2ogqeb. m r liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° : qt fq;;kay-uincline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient ; kfauy;qt-:q 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 m*9 uin*/zbyvb0/9+oj hhtjdjr2pt 1a helicopter of mass M an acceleration of 0.10 rhub 1 j20yn/toh zbd*9j+v /i9tp*jm g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance ax7m:gih9 m, vs0sdtv q l2*ump8is 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 alonem87uxj lcc93g the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 78ec9c3mjx l um 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 5jetfo(4yoop9(f-yr n0) eeuop -+bka 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 oxygen moleculscc,f 1dy5.j9 zsovy +e, 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, b :; bdf6kg3x f9a6y3ppsmptm2 y what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stokf6v7ix(0)tjenzi y 5p an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar tra.z6)p,gi q.ha2iu ckqveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired fru x*xv0qo+ )xrom a bow whose string exerts an average force of 110 N on the arrow over a distance0 )q+ xuv*roxx 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 backwar/5.iapat l1.rtey bao8q rrc1s1 fw 54d 25 cm when the ball is caught. What was the average force exerted by the ball on thya1clts/a a1 rf1 qob.wer45p.t8 ri5e glove?    N

If the speed of a car is in3k:k/8zu gbzscreased by 50%, by what factor will its minimum braking distance be increased, assuming all elg/zs buz8k:3 kse is the same? Ignore the driver’s reaction time.

  At an accident scene on a level rojr0j bme1z7-uad, 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 0.42. Use these data to determine the7rez-jmjb1u0 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 *r ,(*b5a iqskdn4k,ryg9c oyhir6w: of 0.25 kg is pitched 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 plate and the wih*4 ,(n9g ,:k 5yrskqdy rrcib*oa6 pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thro7ng tw --0zxlfwn straight up by someone who does 80.0 J of work on it? Neglect air resisnz-tlwx7f g0- tance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration s ;aggb1d b3uei(6xn: by a single cable. De:6;u d3b1(bxia s enggtermine
(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/ojq6wi ;e0xaaa pk(.)lm10xw m How much must this spring be stretched to sj0xaa.qkp 6e wi;0)w1 ol(axm tore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is tsw7 b76 +nzhhk4pc3 gqhe change in potential energy?bhpzcn3 + 7 hqs6wgk74    J

  By how much does the gravitational potential energy of a 64y2syvrj,a 01v:xi1bbh g+2 on-kg pole vaulter change if his center of mass rises about 4.0 m during v:i1 j12gha xo+rn2ybbsvy 0, the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/dej vtc7r vjs4l:+*d.h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of s 7 tjvrd d:.+*clv4ejthe spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg b)bz5kwv(y43)px kq wbook from the ground so it is 2.20 m above the ground. What is the potkw) bp 3xz5v(qy)b4k wential 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 mdj jfd.nl/2x: 6 5+ql*mzt0dzpof-zt d-c u-elevation of 1600 m and climbs to the top of a 3300-m pxct jz u0 *o dmtm.-dl/zp+:fj- nz65l2fd- qdeak.
(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 tb,1 5ybvrvx d6he 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 ruler marks rdb6vxbv, 1y5?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) andtspq, o 1q 2oki110nnc grabs a vine hanging vertically from a tall tree in the jungle. How high can she0np11,1 noqsci qt2ok swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starthb wfz/9 yj6xv 67j0hying from 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 frictionless 28.0u*fvmv-wp 7 rsqkp2i7k.5 zs .esxd.($^{\circ}$ 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 into0be3b fc6.zemmrs/o(5 hm)v j gravitational potential energy without the aid of a pole. With what minimum speed mustrbf/bs(m60 vcmjhe3mz5o) . e 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 xl1i i3n 4/jt jld7ck/t 4re.rupward from the top of a platform with a speed of 5.0 m/s.k lnj/xrle /icitt17 3.j4dr 4 ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring stiffness consgux:2aml1s oa4wl.- s+ zh 7rmtant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.3mz- .agalh17w4:lr+mu 2xs so0-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track ss w/j:m41p a)ccr xy;khown 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 muc kx;/4p )wca 1jy:srmst it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness constaxn8:lly a-:n7 dal6qfe*uwle7l(; mnnt k), Fig. 6–40. T;ll8lfalnexdnl : * : 7mq-6ean(uy w7he 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 9xo..bwao(gi from a bridge. She is tied to a bungee cord whose unstretched length is 1.(9a gow bixo.2 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 2l36ffxp v uc vgi+3ml1+oykwgg )41sis dragged up to point 1 where it is released py vk+csl v1 2wg fgl+fg3)mu41 6io3xfrom rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed mz6)1v hjr )hzof 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an elevator l/ z7-a1 on9zfrm6pq,spz, asshaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value th /zazs6s ,qpnraf9 -op m,z7l1at the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7/2qd 0iu w0;a o +qlh;x tl.xrmuqkq.6.8 $^{\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 travelin x:r6q qa ei8cy7p8v4xg 95km/h in opposite directions, collide head-on aqi:e q8 874yx6pvrxa cnd 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 avd k x9kgkb:t mi)/xc.8/ayrb a. ,m2dnd reaches the bottom with a speed of 2.2m/s How much thermal energy d)x i9c.:vyag./b2 ktrmx/8 kmk adb,due to friction was generated in this process?    J

  A ski starts from rest and sl43onfgb1c(e;sc4 gisz 6 q*o fnfn7*lides 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.pwy)m l uy*0p5bb t68x0 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 heigkil :p:adg)m 5 / ds obw;8wd8qjj5k6bht of 2.0 m, and it bounces back to a height of 1.5 m. wp:d5 bd5qos; 8am/6wgd8ik) jjlk:b
(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 constadc 9oa9fdu k .z)rka8*nt horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coeffici*8a )kf 9k9rduzd.coaent of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes pointf -b.*agjqz* :whk;yh 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance trk:h y;g*a-jf *hzq.bwaveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of;ak/1qzy0ey);s ac0 yt 5gg :1 dpzkwy 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 attachet y:omqw/s4j-9-,hu 8wkwprl d to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium poq 9j wwoy/--u, tm:r8hs4klpwsition 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 xknsg8, 9nhx4 to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond s xkn8h4,xg 9nits equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg h7/x,h0-yvkhaxh mw ( including , 7hy-vmw(/xaxhh0kh 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 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 t*daf)c5o i,yel)s hc*o a sixth-story window 16*dci*)h 5 el,f )acoys.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what mustbh. ) y; m3a:jilsxo; ny/cp)e be the average f;)p.n a)j/lyxhmyo; 3:icb s eorce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports carp0jd(e(z-eez o9u pt+ accelerates from rest to 95km/h in 7.4 s. What is the average power delivered by +u-0(p 9jz( peezode tthe engine?$\approx$    hp

  (a) Show that one British horsepowfp2 ;)p*hyuzr er$ \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 “kilowbj z+e0 id-qn5m q5bh;att-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 65kmpqh4b 2dgn: +x/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at n2g:+hxp 4q dba constant 75km/h.    hp

  How much work can a 3.0-hp motor do ink/co3xs )0+dq/bp dtu 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 motikz/ n+n6/jqpwp8d8qe on takes 1.5 sep6kn z/ /dn8p8w j+qq, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. Wh-5c txoy8d8ml at output rating (watts) should the p yoxm -58ct8dlump motor have?    W

  During a workout, the football players at State U. r1c0gvg:lwd, 4okh:z s;f z;zean up the stadium stairs in 66 s. The stairs are 140 m loncgld;zze v:fzg, o:s0;4whk1g 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 a 37p6 wcattjz7u,iqem3qn9h9 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 l 24rdrs/f ut.16- iimql,bwisteep a hill can it climb at a constant speed of wr.iiq4,/r2ll6-uitbsf1m d75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to dramdoh;ttc1:/h9 zw 2;lj4c /benq r/pag a 310-kg box along a level floor at a speedthe4 /nj; 1 phlar/:dzcbq; w9/t2mco of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 75htz5c qs0iua6y3h e1 .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” quu1 u;n kpey407) qgothat are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the 7; q up n0)k1qeyug4oubumper 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 10szbg((3awq :d.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 fil(3qa:db(w zgsl 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 7*lm y:h yz51brz(yeh (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 speeyy*b7hzyhrz5 ( : mel1d 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 loope us l8)zyaj7e6d track shown in Fig. 6–39 is to remain on the track at all times, even at j s7euz) y68althe very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his pfsh. vb/. mfq5wz5 g)ilc(,do;fs *pzarachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminall,z*fi5v(;d h.c /sf fspmgq5wz b.)o 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 m sghm3x3 v8n,of length L whose other end is fixed (Fim3h svm3xg 8,ng. 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the;qzstsywzb3+ ; krv76 top of a 3700-m-high mountain. The climb is made in 5.0 h startingsrv6qw+3bsz y ; tkz;7 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 elel wi9b vf1v0o8vator 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 claims that its lifts can move 47,0gckzx1k:jo5:i*3g h bqvr 6*j 00 people per hour. If the average lift carries people about 200 m (vertk*5:rgzqx c1bjkj 3o*i6g: vhically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m befopaux73g r7i92hzh.p x;zw*b wre striking thprwa;z7.3gi h 7xz b*2puw9xhe 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 r5+:-+jc* bqah a hz3ukge gm1circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go5aubgq kr +3-agc1 hmej +h*:z through it.    mg

  (a) If the human body could convertzd;utc n3s *2x a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one n3 x; stu2dcz*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 et.ww-4tql6, zv (vrkupward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, t 3g sl+8umhls a9m)kk6he spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scsks khu98ma3+6 ml)lgale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. 6–4p3td p5;(gcc,aauu+a 5). He releases the rope whp+t5c,;ad( 3cu gpa uaen 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-kura8mc(1 u j y pc1,g,n-9hgnkg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish th9nuch8kmc,yj1,1 r p a(-gugnis feat?    W

  Some electric-power companies use wrhqs p1+0tv u)ater to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To1)sq r+0t phuv 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 cutt (d2*x3psr/74nfldwe 66dxeg ou. p s in half. What is the spring stiffness constant for each of the two resulting spr67e6/2ndxpu*r3tg plew dsd o(f x.s 4ings?   k

  A 6.0-kg block is pushed 8.0 bcvn: 9 mcbzz )*7c2u b+sn0cgm up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate fr 5 4ev az0-2ervzp:kx2 -unfteom 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to r40vte pavk52-f z-eeu2n zx:75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (gn))l (e x ip;p7fiep)the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient whenp;pxeg( iel if7n ))p) 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 a distance of 500 m, wha fwyg pz702(0iram :vixz*( zat was its velocarm 0 7 aiip:(v2f yxz(g0wzz*ity 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 wg0d h8jv5rk s1q*9ott),pamrheel from a height of 2.0 m at a rate of 95kg/s (a) If thih0sr 9t pog j)k5rd 18*,vmtaqs water 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