In what ways is the word “wd8;5/ccb:k vh t iyyb)ork” as used in everyday language the same as that defyhcb;/ 8)vkti5cb :dy ined in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do wor3jbw vuqr9v29a-7bj gk on an object? Explain.

Can the normal force ontx*uum awl ep nu7-060 an object ever do work? Explain.

A woman swimming upstream is not moving with resped 6y1vs2,w 8 x/tu8e 7oaskxrmct to the shore. Is she doing y sd 88tr1sxvawxe/,27u mo 6kany work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces alwayjytt gmb8w(ok2+ 6 3mhs negative? [Hint: Consider what happens to the dgmb yhk 28+(tw6m 3jtoishes when you pull a tablecloth out from under them.]

Why is it tiring to pushc zisv(rjo-dq38yeq)gh 6v-a, 6 -q cl hard against a solid wall even though you are doing no v-a o c 8-crj(-ygs 6qliv6dq3hez ,)qwork?

You have two springs that are identical excesrs :4tlf u5g1pt that spring l is stiffer than spr1 lgt:u5s sf4ring 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 forcg,t xp,4palj xpa1( 0qe on a block that is free to slide on a frictionless surface (Fig.6-30). The bloc qajax0,pp x,(p1tg4 lk 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 gravitati8b,;ta d yor:honal potential energy change when you jump as high aho,a ;rb:yd8ts you can?

In Fig. 6–31, water balloons arefs 8b qzvu lt a8gu:2hb/8prfea.6e,0 tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the hige fuqfe6bg v,:.88zap2/r 8lbsht0 uahest speed on impact? Ignore air resistance.

A pendulum is launched - lnx ,mai fo;ustd3:-from a point that is a height 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 along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium piu:xm lofd-s,a 3-tn;osition? Explain.

A coil spring of mass m rests upright on a table. If you compress the spri2owxlh )b qmo pfu2h3p,1;, fqng by pressing down with your hand and then release it, can the spring mp; u3lbhp qoq ,f,)hox22fw1leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ce8fdz h:-lu:so iling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against:dul h8f o:zs- his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy whek.sux 5:q0z lh+vg3 ykn water at the top of a waterfall falls to thx5 :+0.g h 3szyvklkque pool below?

Describe the energy transformations when a cyx4 b5k*ack:j.td732tkg e z child hops around on a pogo stick.

Describe the energy transformations that take place when a skier startc7jle+if5; d( u7agfxp-w9j ws skiing down a hill, but after a time is brought to rest by sf7 5gw wu;(epdlx 9+fjj a7ic-triking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a2g.himlr+ 19i 8sosi 7btu,y p 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.b 8pir+ msly179 i,uiso h2gt and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in92ja)qo n4i gw their path rather than stepping on to) q4a2ino9 wgjp and jumping down on the other side. Explain.

Two identical arrows,)wtb,wkm+d 3m one with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts awm )+dbw t3,mk constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms rbj; jc-uhq ba9 a*.zew n5p(2of energy, (a) ignoring friction, and (b) taking friction into account. Explain whyheb-jn;(.qp 5j bw 29acuz ar* a grandfather clock has to be wound up.

When a “superball” is l; nit7*8 ww, njr8yt5t;m14o)c+x dnmpivahdropped, can it rebound to a height greater than its original + ;a, w)*tmcp vny t48jrd; l5n87nmwh1xtoii height? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on +go7gsgdt fn/kc. 4 hg;6)zm 6jlas) ithe suitcase depends on which of the following: (a) whether you lift it straight up or along a more co gs6gi )gdm 4ltzghnosk.a c6+/fj;7)mplicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the s:xc5*s /d /w8p ijxpipower needed rather than the work.

Why is it easier to climb a +;.p r9y1g*qz eio penmountain via a zigzag trail than to climb straight uop;1*rz.einpqy +e g9p?

Recall from Chapter 4, Example 4–14, that y lbn ie+f *o4;qmm:a7ymte7s, ou can use a pulley and ropes to decrease the force needed to raise a heavy load 7tmm:e+fs m7b* ynio ;,qel4a(see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravb/wk1vmk qv(qhpc,(5 itational force when a 265-kg pile driver falls 2.80 m?,c b/h(p mk1 5vw(qqvk    J

  A 65.0-kg firefighter climbs a fl773p+sgrz pe kight of stairs 20.0 m high. How much work is regp3spzk7r7 e+ quired?    J

  A 1300-N crate rests on the floor. How much work is ret)df *x- gktq5rx-j k4quired to move it at constant speed (a) 4.0 m along d4tkxk xjr )fqt-g5- *the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the mo ecm3 c4 alwuc907ad14ru9u szvers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction wa199rcd3a 7use z0cuaumc4w 4 ls 0.50?    J

  A box of mass 5.0 kg is accelerated by a force acr +ysi6atptfay u 812h6oss a floor at a rate of for 7.0 s. Find the net work doah ytfy ista28p+66u 1ne on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a fnulur3h loor3a1*)h: sr*v 7table. How much work is required trsol3*h *rhoa fu7r:v 3)l1nu o stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used tp.:i9j )bh towyo7c3 ,fiq2pw o liff objects we might not otherwise bew 27ifjbhity 9:p3p,o.oq)wc able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from accelerating byi d4mkp*i4ycb8fqh 0ujd7 ;e: a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective mj84 0c:; 7id4phdyb*ukqfi e 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 helicoptevij4(wvr )f 7xr of mass M an acceleration of 0.10 g upward.ivjv rf4w)(7x    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 distan53np93/br-rtr u7 aklaik6xs ce axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fizgrc w p736 mq2lyv*0*l2zjgjg. 6–37. Determine the wo6jlg2 0z7g z2yvw*3qcpl*jrmrk done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a parti0pcdn my36sj9cle 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 molecule,f10hnph v;-ggn,+b y 6 ziiz1z 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 oyz9ahc mm 338has 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 electron/lr+j: qm3aq suigd e.a(k v** $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 akmz(n6 lna4d) n/8kvvt 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bov1 d6 van7dt7ew whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of1v7 dvnta7 6de the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glob fw2e df0)ot:ve backward 25 cm when the ball is caught. What was the average force exerted tf f:0oe2wbd)by the ball on the glove?    N

If the speed of a car is increaz:z*:x2w;kz+hlweyg sed by 50%, by what factor will its minimum braking2* zx g:hww;:+lzkyze distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigakc wifppr rd/;;:8kqdzek;y rq;+.sey(r y,3tors 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 thekc:fe8+dr /;ry; 3 ry. ;yk( pz,sipkwrdqe ;qse data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reach xer(ajdthj*9/ frrqm(:2sf; es the plate, it may have slowed by 10%. Neglect redj(;h fj x*:rta9/rmfq2 (sing gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown str rja6-puc a et1vn;/z*aight up by someone who does 80.0 J of work ojnz/vp c a;*- 1r6eutan it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vert-m;esaxl*,kz w :k2b qically with an acceleration by a single cable. Detex :lsak*;em2 kbzq w,-rmine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much muscny h;k-fx.6 lt this spring b. cnkxl; 6yh-fe stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one fr ge8z sj)0y;7u9yaq g7 ldc +kitvr+-.r up6branch to another 1.2 m higher. What is the change in potentisfj i7kpg y9c zuu+a0.t y7-+der r;l q6gr8v)al energy?    J

  By how much does the gravitational potential env7r *r4iun5e oqh5m,sergy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m durin,* uo 4rn5hrem5qvis7g the jump?    J

  A 1200-kg car rolling on a horizontal surface has s- lllxck7r 9704 grygspeed v = 65 km/h when it strikes a horizontal coiled spgr0rly cxl9-4k7 gls7ring 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 ground u8xq1apaj exii8kgn4 l ,36v: so it is 2.20 m above the ground. What is the potential energqiugxe8 j3lan a81 pi x,4kv6:y 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 ako )ylg4rtob u/8j j(*t an elevation of 1600 m and climbs to the top of a 3300-m pe)8 kj4 *robt(u/oglj yak.
(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 er8- gn2efpxl( nd of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the en28lepx rg( n-fd of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a 4*t; qub;dbgndj;fq;wi9bun11k 1 hwvine hanging vertically frqnd;d nu19;jgithb qbw1; 1w fkbu;* 4om a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting fup h, t34rjz ed-ia4-s 4-i go+)licberom 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 giveoe p b9o-97dthkdv4 bj*s i07ln a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic 87gn o;vswc8nenergy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.78cw78g o n;nvsm/s.    m/s

  A 65-kg trampoline artist jumps vertically upw2 ;rtd6ebq 5sqard from the top of a platform with a sd2s tqr q5eb6;peed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constant is 950N/mx6)luv 5bnra/ c5+vuq is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg bu 65cul)b/q 5nvxar+ vall 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 track3mt+tw* 2h/*xy 85rrwso iixms;szw9 shown in Fig. 6–39. If the blocxst2s wo w*m 8t/r3wrih*x;95m syz+ ik is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end ofa3k.p x;)jozc *+r8 zel g+krv a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial disp8 o.x rc3gzp+levz *arkj )k;+lacement $x_0$ 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 cusxz36te) 7kil bv71a bridge. She is tied to a bungee cord whose un 13uszc)ek7b6x iv7tl stretched 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 applies. $\approx$    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 where it sm utty: 6,jlx ;3;iec-1jia zis releasectt1i x,zjs;y ;e:3 ma6 jul-id from 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 of 12 m/s at an angle of lmb:9 oyc/f-y2i j;zb33 $^{\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 thb5 gw0f3l:ano+ d -ggezj- 4cee 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 when brought to rest. Let M be the total mass of the elevator and passengers g 3cg-fj ln gzew4bo-05a:de+.

  A cyclist intends to cycle up 8yzy4 ktu 4e0oa 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 95km/h in owatlb2o. ufv+ 2 )amw3pposite directions, collide he )t f w2u+vb2m3owal.aad-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reach8mt/pch4o3 ts es the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this process? tp m48/3oh tsc   J

  A ski starts from rest and slides dowa/6 8k85 x:mtp,wzzd cbaw xms j+be)*cia8 0xn a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m abovk6mj1 bssn m5 wo- rjg9/t3(bwe 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 bouncesbg f10 0/zpyff back to a height of 1.5 m. gfb0y/10f f zp
(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 from8dmzz21 s+1bamh rp5f rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed 1+5p8asm2zrmhd z b1f of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of 28 y(elbjw;qijpv;-gzd8( il f ;-hxp If the average force of friction is equal to one-fifth of its weight, with what speed willh2 ;xbdf;l wp;v-qiep8(gz l( 8j-ij y 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 1lywj.s;il/;c* t ve l.8.0 $^{\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 bloc 6ni40;a g,axe-q ti09dlygzbk is firmly attached 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 position before stopping and turning back. What is the coeffd0la,qgxg ib; n60 za4-ty9i eicient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a vezy hr ;/;j+ i8hpzmtdj- 5ncg0ry 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 its equilibrium position wim /; 0y;zjpg ncd+irhjht-5z8ll it stretch on its first swing?    m

  Early test flights for the space shuttle usede1 iy zgxcrv0d 8 (4m6t,jazu: a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eve za rdj(1x,v64ui e:mg8y0tzcntually 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 2;8b;*ymgzbxi td )1t /qurm kto lift a 315-kg piano to a sixth-story window 16.0 b82* xu gzymr;dt ); ibtk/1mqm above?    s

  If a car generates 18 hp when traveling at a steady 88km/78 laj4l1djgy rg z1(zh what must be the average force exerted on the car due to friction and air resistg7r lazyj(11l4j gdz8ance?    N

  A 1400-kg sports car accelerates from rytfhsj46m 4ao v 5q42oest to 95km/h in 7.4 s. What is the average power delivered by the engine? 4aj65q 4vtsmfoyho42 $\approx$    hp

  (a) Show that one Britis9)x/6qa5 qsek:nc b beh horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatto6lwl0 een-3m -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 thavutl: 9t*-t7v2v r zfmt her 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximam2vrf t*7lu :tz v9t-vtely what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor (idj)v tfir+4 do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motiojiyhqhk 0-7 p.n takes 1.5 s, what average power y- iqkj0h.7 phwas developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minu1 v+yoc6j+hj45 jf xxw)7tvicte through a height of 3.60 m. What output rati 5ojv chy+147ijx6v j+cfw) xtng (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the st 4j8vv2r :,-wm )cm.o)/ kxjhex olodhadium stairs in 66 s. The stairs are 140 m long and inclined atk :hv,jcexwdm))8xoj. 4 o-olmvh r/ 2 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 aatwg6)a 9h4 s(rnr chfu5 w1.s 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 maxp q5 zzs i)tj*ap-5jm5imum power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the fricj5z-ap )s*j mi55zqt ptional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to beu b8)kmu -6cx8c. jr*fo8 rvyz able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficjmyf.rr8 6u 8x-zcvuc k8o)*bient of friction is 0.45?    hp

  A bicyclist coasts do2 bten/9.f8;euy/yk8 3j7bt wx ;t+dewhkjhmwn 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) bumpers” that ar0io 9alo u7gziaj( 5j0e designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramma(o57 a l90 j0guojiziing into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is gd--jit lfe;; 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above thef;ieg l t;-j-d previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olyma-kyd1ns9fre p 8q*j,pics shows that his center of mass rose 1.1 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 ofnf9jk1*srqdpea- y , 8 the arc?   m/s

  The block of mass m sliding without f.lgt,e1tb n7driction 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. tn,1 gd7te.bl
(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 fell6u :nxy .ny)rs 370 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, ny .uxr sn)6:ycreating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(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 horizo nes5w d,0v ,l5)3p7mgvprd4p xo se*antal cord of length L whose other end is fixed (Fig. 6–45pp *xls,35na4 ,vdsw7gp e 0e mvdro)3).
(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 climb is made c +y 7*u19pmwmgkmeimlr61aq m77 c/-y*yztm in 5.0 h stazm+ekwc cm*1aqm1p 7/t iuy9m7m- yr*6l7mygrting 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 le 0,-csq(d.9xnjy phm 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 cbv7. )u3qtvx qlaims that its lifts can move 47,000 people per hour. If the avq7 3ux bt.v)vqerage lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertic2ji/9*d -8vkg wz ybzeally 81 m before striking the turbine blades./z 2v dek- i8*9zjgwyb 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. 6–44), th; r(r:ldlk s+l+0l qzj.lg ug5e difference in your apparent weight at the top of thg l0r+l+lu.5g( qk;l r:lsj dze 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 could7z xzw) q+ue5c:wxtbx(/w a7b convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he werbxu7wbz ()wza5x :xecwq+7 t/ e fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward5 0l )ecq4p2tf t6uxuh 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 bathr jex,qv(2+ ttn*mvi gd)w, x:room scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m,,vrm)xe :tt(2ij xwgdv ,+nq* what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a i ns vawh)ws4+s/ (ee)lake (Fig. 6–45). He releswi e4 (/+ wv)hss)eanases 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 ver1u; ;ic *btx2dgqll d(t0rqv2j+ xub:tical distance of 5.0 m in 9.0 s. What minimum vi2xljd:tqb+qxug01bc 2l;*d;rt (upower output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped *iq+nc vp7ug .by reversible turbine pumps fvcu+ngp qi* .7rom a low 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 i1-v.qp z )kaoxs the spring stiffness constant for .)oaq -kvzxp1 each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up 8p+6 njo an/pta 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 accelerad(5kaw5. ;vghb z2gbk47fz*u5qr bgate from 35km/h to 55km/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 frictional loswk a57. rgaz5 q5*ug4ghk;(v2bzfb dbses.    s

  In a common test for cardiac function (the “stress test”)fd lb 0us s9(*a.uhmt358wu3r eoz3u b-qj+gg, the patient walks on an inclined treadmill (Fig. 6–46). Estimatou3+b8gr3wz( lbt3 .u eudu0 - qg9jshsm5fa*e 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 /o1f3 x,tdj .zcnu0oe vertically upward a distance of 500 m, what w0ocu f1xjdt/ 3zon e,.as its velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at 5r sbvhc/x, 4pa rate of 95kg/s (a) If this water wheel ischrx pb,v 45/s 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