In what ways is the word “work” 2 gg:jn::rc wd;aiw,2w uyca 2as used in everyday language the same as that defined in phyc,g a rd:g2:u2:cwyn 2awjwi; sics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Exa f znx.e*bgw9zfc:.5 plain.

Can the normal force on an object s/og0 orln be6-yd:hz 5f 9.nvever do work? Explain.

A woman swimming upstream ilf3psx snsx/6qb-f 6pd5k id7t )5 c(ss not moving with respect to the shore. Is she doing any work? I6 q (nip5ct3)xsdfxdpb 6 kl75ssf/-sf she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consi r5jbrpj0x kz9f,d,f) ,dkv ,xder what happens to the di f)k,px5x,zbjjdk0d ,9fr,v rshes when you pull a tablecloth out from under them.]

Why is it tiring to pus3 vdbu d*ycykkth10 sr .2h.)ch hard against a solid wall even though you are doing no wouky c1k.h. bhr0cyvd)sd*23t rk?

You have two springs that are identical except that spring l is stiffer than or3ev8v p*s ezf1,mi2spring 2* e3msiz,vef po1vr2 8 $(k_1>k_2).$ 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 blvjc c+38e +;okooi)yj ;0wp xeock that is free to slide on a frictionless surface (Fig.6-30). The block starts from rp 0jjc;ic ove++oy;oe 8)w3k xest 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 chanzz)8dkv7 :i,n p yi7bdge when y8v)d7:zdknp7y iz i,bou jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof o eutn;ut b5by j1w40l:f a building, all with the same speed but with different launch0;l5:4t1wjuutbn y eb angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launche-j8ysx h( xr 0ivvixvf)q3 0:ed 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 traject:v i0v x3e)xs fjhy-vq( xr08iory. 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 compresshf9qt/.ubol vn2 , x;t the spring by pressing down with your hand and then releat lf/hq ;.b,ovtu2n 9xse it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel *qn/x(+ 7tjy 7sq c rq* owd:1;zm0jo qmzcx5gwire (Fig. 6–33). The instructor pulls the ball back and stands agains gx t7 q5 qjj:;*/* wcoxm 1cz+o0mdyrz(7qqnst the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy whe + qu3dfzst .3yt cee/zbu1o5+n water at the top of a waterfall fal/+tbst uqe+o1 z .zfyd35ue3c ls to the pool below?

Describe the energy transformations when a child hops around on a pogo sti e2mjao(nk,d7ck.

Describe the energy transformations that tak1rq dr (by.suz.9slm. e place when a skier starts skiing down a hill, but after a time is brought to rest by strikingy( 9 rls..rd zmqs1ub. a snowdrift.

A child on a sled (total mass m) starts fro oa*.y b0sq9uhm rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on theo .qyb*hs0a 9u angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen loahsiy wbc; 5.1g in their path rather than stepping on top and jumping down on the other side. ; wc51bsahyi.Explain.

Two identical arrows, one with twice the speed of the othc( ya 2h.40gk hw: evsj0kyin6er, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetr: c s .nive4ak0jy h2g(60kywhate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energ+ bpeh5cszg8 eu x .ob6;jw5 pb0xln5)y, (a) ignoring friction, and (b) taking friction into account. Expx.+;j5u pl ces no)exbg6b5wp0h8b z5 lain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it reboun1(nb)u pre ho wl8gchau* z+pw/ i5.2ad to a height greater than its original height? Explain.e n1goalpwr(b p.*+ hzw5h)au2u/i 8 c

Suppose you lift a suitcase from the floor to a table. The wor7 5yao8un 1uboj4)je uk you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path,o1uouj au4) eyjb875 n (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed ratx*-evdrxf-(gy* i l7 dher than the work.

Why is it easier to climb a mountain via a zigzag trail than6uvav1uo- yais s/ 8b t4sl5ib,xxy19 to climb straight u5s1 iiab,u syx9 aov1syx/vtb 4l68-up?

Recall from Chapter 4, Example 4–14, that you can use 7b6loak.3fg aa pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the ga bol7k3a 6f.load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitationalf9r, o b,vong 5+a+fgo force when a 265-kg pile driver falls5+naor,f ofg, bov+g 9 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of sta32 yg +yk9eftpirs 20.0 m high. How much work is requi gt3 ykfy9+e2pred?    J

  A 1300-N crate rests ocdpe vgolo c (.4*y53vn the floor. How much work is required to move it at constant splgvcpe4vo*5 3o.yd (ceed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the mo)d 9 az2jy,ayub,-uh6bend; xvers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleray)h9uy-deb,6 2nua b; ,dzaxj tion, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a forcez 4 c lncetj.xv 1f9gjej:+72ficx6;g across a floor at a rate of for 7.0 s. Find the neeczc.e2x61 ncft+ j f j 7g:lvj9i4x;gt work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie -j rb62bhos1 fc9.sxre)tci3flat on a table. How much work is required to stack them one on top of a b6o-x9ih2te3rbfcscr j)1 .s nother?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects *i qmd7go- h(cwe might not otherwise be (7-icqd hg*om 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 accelera t ,2eupz5,mbgting by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0tzb pum5,,g2e.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 mass M an acceleration of odqixo .b/3 9r0.103./bqri9oxdo 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 axis is linea6f1cd1ot5h0)i (jx xztd pwc0r 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 e9z9au1tz ,lgaxis, varies as shown in Fig. 6–37. Determine t a91u 9tl,ezgzhe work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a c f *8qr:3y.qc )6 pp7uftvpqrparticle 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 moleculef 6 1nybgcm75eq*sb8s16-8i njsf s ak, 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 wm(+ wrh)cxa q56 jrr4ohat 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 gt+nh up,v;0fb,pp+ 5l.wpit 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-kgcar traveli- x e(l*sk x55knrne 8-z(hgwdng at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whl 62wxi oq3)zlose string exerts an average force of 110 N on the arrow over a distance of3lzw6 xilq2 )o 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 fi82 i+av6oa ;umthu 9xgelder’s glove backward 25 cm when thtv;89h amua2uxoi+6ge ball 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%, by what factor will its minimum ovq2ic (xv(+yr.u 1xqbraking distance b+yq vr iu(c12(xq vx.oe increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skidm)rzhrv::tnt9zb3/ d mark to be 88 m long. The accident occurred on a rainybvtn:/ rhtz r)z:93d m day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver 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 pitm;-1k4 fg n2 semghdu2,x.fdyched 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 betwe.2, ;e2k mgyh 4xg -uff1smdnden the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown 7.4h+)3pscz rsox0g hyi ,4 8ekvpp sastraight up by someone who does 80.0 J of work on it? Neglect air resistan74 ipp cea)yo0s ,.vspksgxrh 3z8+4hce.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single cabyu+a,:cw.n cas, k 3z:u5pqkhll (nf:le. D:.k:n,aplqs(uchucly5+ :a ,wfnz 3ketermine
(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/4 /yfd odx(bci(as)x -m How much must this spring be stretched to store 25 J of potential eneoi(/x s dxb-dc)yf4(argy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m;; :ill+ bvolc higher. What is the change in potentv o;bcil:+l; lial energy?    J

  By how much does the gravitational potential energy of a 64-kg po9kq. ujcp40v3ibq +lyle vaulter change if his center of mass rpk+ yc304ji.vu9 blq qises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal fie q(s9;)y fz n4vbw8surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brough;ni9bv fwyz(s4 e )fq8t 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 bo6 knz,7soux j5ok from the ground so it is 2.20 m above the ground. What is thkoz 6 jsnux7,5e 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 elevation of 1600 m and climbs to the top of gl q:p6;vup.va 3300-m peakl uv6pv:gq;. p.
(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 verticale2w0 *a2d asrsf:1lnl k27zasly next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now f0aas:ra2w ln 2dks1 szl7 2e*attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzanbl8ozs h5dwlgm8:c .7 2kt*ex, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she. x5mg78:k 8ll2*dbezt oswch swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, startingjlh7 *dcves+i.-lehnv11u- x 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 givec*ok;. w9 8ct9prqx xv0kjn-tn 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 energy is transformed into gravitational potent02xx-6ix nwk .t1 nkrpin, i*tial 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/itxr,n6- ixkpin nw0kxt*21.s.    m/s

  A 65-kg trampoline artist jumps vertically upward from.rz9t, d3b33n3xkbav vq k zjp b67:cl the top of a platform with v kqcbd9,vp3 n3bbz rx7 6.z3k3ajtl:a speed 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 )ku adc9u 1n5yspring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) ukundayc5) 91 What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped tqgn5lcah/fh.n3 t *s+7dwxh(yk 4 on.rack 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 it be fh.hs n+t7lngaqdkoy (ncxw*3 5./ 4hreleased?    r

A block of mass m is attached to7a0 sxh9o(,pcmjf6x i the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displaccpjao,9h76sx (fx 0mi ement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whose ut z+ 90rl)yem02qytpu nstretched length is 12 m, and falls a total of 31 m. (a) Calculate the sp2ur0 zmytl+ey09q p)tring 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 i3qn.xyua f)xz2 9 p (d8bxw*px9dc6yc s released from rest. Assuming no friction, calculat8z*b2yac)q xyw 3c(6fp9u dpnx.xd9xe the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed -agvupqo9 * kkh v2fs(1u7na (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 placed at th 6mzpz pt13v47w9ro yqe 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 379zppt4o 1zv6wmy rqconstant 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 7.8.i4n :mnc .vpc $^{\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 76502 pvr(xv )d5rb;sjdo 0 kg and traveling 95km/h in opposite directions, collide head-on and comx;0(p2sjbrvo5v r ) dde to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a sl fi );s,5cdbiqide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to frict,sbcdif 5;i q)ion was generated in this process?    J

  A ski starts from repwn94gv*y xyfm. z 1o9st and slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the grwmv01: ukrcw;hw: q*g ound.
(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 itdzmnq 9 rdisi5+4 cf4v. ci83t bounces back to a height of 1.5 m. rq i4z .4i8 scdic9n5+tvd3mf
(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 ac:k/bf-gk y y+ u4xp*osross a floor with a constant horizontal force of 350 N. For the first o 4xg+yk: fskb/y-pu*15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If ysbd;q6g5s6 mubtoj qfd :w:*klw-. /(vb /j ithe average force of friction is equal to one-fifth of its weight, with wty(/:bijqogb/;-:wbuds v jq.f*wskd5l 6 m6hat speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s-7 foyb(*dij j reaches 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 horizontal spri4pyhk*eejj(. anyv*rcjr+ b4j je1 ac d 1-1r9ng (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 p*1j a yr1j1ecbj4ve* y+r(crj 4.d9nk j- heaout 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal*rot8o /u1kd2 w- kdbx spring, Fig. 6–40. The block can slide along a table where the coeff1owb-t/ * 82rxkd kdouicient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 k qu7znsh e3(h5g 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 luze sn7hh53( qanding 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 ad) o1l oh dix9l.dr9 2lse)ge6 1750-W motor to lift a 315-kg piano to a sixth-story window 16.0 mdh)lle 91sdo2).o r96li edg x above?    s

  If a car generates 18 hp when traveling at a/d dkc l1*wv.p steady 88km/h what must be the average force exerted on the car due to friction and air/.1dpwk l*cvd resistance?    N

  A 1400-kg sports car accelerb bwzqhqfu2 ya1d ( lc1c2;21nates from rest to 95km/h in 7.4 s. What is the averah q1 2blc2q1u1;nb wfc a(2dyzge power delivered by the engine?$\approx$    hp

  (a) Show that one Britishtmu4 1acah;hs;; ;od s 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 foriiym b 3 m+ty+v1c:kmoo8e5:k m of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slowsqhh*ny*s-k-ckz+hu0;5pvv q 9vz ge6y tp(4t down from to 65km/h in about 6.0 s on the level when it is in neutral. Appr yh gksp 9v qc* htqu0--+kzy;v(5v6nzpe* h4toximately 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 do in 1y,.) +3 /.zgzcj:t njmiyfuve.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14me 2i(qu fz7rb.yp09pg /s If this motion takes 1.5 s, what average power was d0b9zgeufqp i.(p7y r2eveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minuxc 6xz qp(z/ju6mt7s 64b hc9dte through a height of 3.60 m. What output rating (watts) should the pump66 xcdp9 7q6m czxhbts( zj/4u motor have?    W

  During a workout, the footballn(nl l ab-2lsd+6; gvd players at State U. ran up the stadium stairs in 66 s. sl;- (nal gn+db 2dv6lThe stairs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist cliow/jspt 7 z f21t;zkug0-zf e1sn/o1k mb 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 out2a;sl.kadb usrdf6us 4*q ; /sput of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frak/64ab .dfr s *ls;s2qusu;dictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box alongt(kw7yw/,*; vd gxncl2dt m9p a level floor at a speed of 1.2m/s if the coefficient of friction is,(d/tdm v;cg*w9k n 7l2ywxtp 0.45?    hp

  A bicyclist coasts down a 7. /z s 2lz1xh:px3fpmv/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’sk9rf(ad6z;ydpl6j7y o,ou i + cars have built “5mi/h(8km/h) bumpers” that 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 elaa+pyzj doolf 66i;(dr,9y 7kustic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the fq 9ueqwza8x5 6irst shelf 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 laying flat on the zqu8aew6x 95qfloor to start? $\approx$    J

  A film of Jesse Owens’s famous lonez:9d2* ) un6oliu a+gddo5lbs.rx3.e tq v-cg jump (Fig. 6–42) in the 1936 Olympics shows that s6eq)za-2bduxc* :oerl5 +. gn3do ivt .d9luhis 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 of the arc?   m/s

  The block of mass m sliding without frictionebunfe9t +h, yg(v3 d9 along the looped track shown in Fig. 6–39 is to remain onfe9e3 (b 9+hdu y,tgvn the track at all times, even at the 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 aircrbj4dv h 7k0z;y,9uxar:nogh1aft without his parachute opening. He landed in a sn:1urynajbo 049g v;h h7kzd ,xowbank, creating 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 horizontal cord of length L whose other end is fixedgk+cypp k-4z1rw kqfd4)of0. (Fig. 6–43). kfr o1)c+4pf y-k.pk0wq4gz d
(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. Tho wc;lo j4myy4./opv ,tyg; 4ze climb is made in 5.0 h s;t;oojo4yzc,.y4lym g/v p w4 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,2;wo(g1th et o 8fu,vzm2 eyi when a 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 claims that its lifts clg wgf*+p +mx*an move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power nee*+xg*p w+g lmfded.$a\times10^b$ W a =    b =   

  Water flows over a da:vlhm*rj19is q vkn3 a-t+d8nm at the rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calcark s-hq+8 *li vd3 1v9j:nmntulate
(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 (2+qqw0z ;bvr,70gr;vs0inyv h; ybzvFig. 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 go y2q7h0nvg0rsvz ;iq z;vbby+0;wv, r through it.    mg

  (a) If the human body could convert a candy bar directly into work, how3 avr4k 6v 0uj tft;tl2n*q*lw high could an 82-kg man climb a ladder if he were fueled by one bar (=10r*4t6wj lvlk2nqf;3u 0t* tav00kJ)    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 upk f2y,)umg :kgg p8qp9ward 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, the spring inside the scale comprm1)guq9jy7tgp k)sz62p - *v vhkln;hesses 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, wk6;ty)2q)1lgum -gj vs9 phk7n pv*hzhat does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig8jt-: yha err xny8 s1*ms8xy). 6–45). He releases the rope when his velocity is zero. -xy)j1xr8 :rhastsne8 m8 y*y
(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 athle-ven8u7p 0 eb3 ug*lj gvlfvs s4a)l,rlo3v-6te climbs a vertical distance of 5.0 m in 9.0 s. What minimum power outp ps6eo*vvb s-ulfr3n0g g3a7e-ljv, 8l4u lv)ut was used to accomplish this feat?    W

  Some electric-power companies use wathb 6f7x8izun; htw6ob x4fw8ekty(, ;er to store energy. Water is pumped by reversibleox8y ;4ezft ,6ntbix( 8wwuk7bh; f h6 turbine pumps from 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. xx:vth0*38scb-jr r ,g, qc )a+hkxfoWhat is the spring stiffness constant for each oforxb+x*)agthf x v-,8ckh 3r0cq: s,j the two resulting springs?   k

  A 6.0-kg block is pu7tya(zp3ge /jutt(5 b shed 8.0 m 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 from 35km/h to 55kmhe 0 639p qy,zfurd77cqw+cni/h in 3.2 s, how long will it take to accep, 3qz6fn+7rqhe 79wdui0yc clerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress tesbpgc r .y+l*fb2(:ts 52ag 4sdx y0blkt”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg :y0bg(d g2a kyscf x+l.2*brpsb5 l4tpatient 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 verticafn ,*hw hsv;(illy upward a distance of 500 m, what was its ,wi(*sfnh ;vh 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 ew3v li)h-tr05mhs3wx xi -3v from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up ihi5vevl-tm)w33w r 0xsx -h3to 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