In what ways is the word “work” as used ib oew k:/e;rd*x qb5re8ycr2qv3 m3 (cn everyday language the same as that defined in physics? In what ways is it c;8mxev23kd* /e qrw 5obbeyrq cr3(:different? Give examples of both.

Can a centripetal force ever do work on a5rda9gz1tn hr/lo6h 8n object? Explain.

Can the normal force on an org+s 6;j7mpcp p1-)ot4* pp/uytdjrz bject ever do work? Explain.

A woman swimming upstream is not moving with dmi(0 8 ;snt p9bvga:nrespect to the shore. Is she doing any work? If she stops swimming and merely fln:0;mb ipt dg9 (n8vsaoats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider ae +ka70l+ m td0tmn3ymr4id*what happens to the dishes when yo*m t7 n3a0tlk a irdmym+d0+4eu pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though1ejb atkc3te09 d .(io you are doing no workd3 01 ecjok.b 9eat(it?

You have two springs that are identical except that spring l is stiffer th+. :ce/v:lkq:z,tfqwd o f;om an springf::f+cd,l qe.vkt/w;:o mzqo 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 force on m3 f-gx7,o0fye-n l2xx q l5qda block that is free to slide on a frictionx 5oy3,f qqx -x0e7- 2gnfmdllless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy c(mn6r rvwel+ 6hange when you jump as high as you can?r+w6lr ne(m v6

In Fig. 6–31, water balloons are tossed frj5pj (n jar44els,:y 1 rg)npgom the roof of a building, all with the same speed but with different launch angles. Which one haprjeg(lj sjnga,4)n1y:p4 r5 s the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowex*wmzwz3pe/(/ :wg3d-j zj kp2tzs/l st 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 upwx3( e / 2tz zks j*zjwm3lzd:-gp//wpward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you comui kq hq;xrg8 vpv:5+6press the spring by pressing down with your hand and then release it, can the spring leave th:8vurk6+v xq;phiqg5 e table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig2kl3 y p+laf6z. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball witf al+3lp6 z2ykhout pushing it. Why?

What happens to the gravitational potential energy when water at th7 5hhcg13am+w cs1oife top of a waterfall f 3h1mh1io5as7cw gc+ falls to the pool below?

Describe the energy transformations when a chilpnl :(hq,nxq(d hops around on a pogo stick.

Describe the energy transformations that take place wh-ijkv*th h3b)hq dx )2en a skier starts skiing down a hilh)ixkbv- qj thd2h3*) l, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts frohwnux + v) .2eb- 5v:n k9w)ui2ilkhkom rest at the top of a hill of height h and slides down. Does the velo2enui)nwh.x k o-9lhk2+b:) ikvv w5ucity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over, advo j,p9 ;p2cslde- a fallen log in their path rather than stepping on top and,c, apvds9oe l2-pdj ; jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other,f,bqpa1w 2u a4+n*s -o;hd wkw are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the fw1;,s 2+d anp*q4-w uowb ahfkaster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulu n:)2sdl9 x dao a3wjlx)w*af3s0kx1pm in terms of energy, (a) ignoring friction, and (bxxw*: l2aondj3)a93s0swf x) kl1 pad) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a heighob6rwo6llc . ,t greater than its originalco r lb,o.66wl height? Explain.

Suppose you lift a suitcase from the floor to a table. The work youv o5w0p/kpgw5 do on the suitcase depends on which of the follo5o kwg/ pv5wp0wing: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the powe:ztf1m p)ir k7r needed rather than the work.

Why is it easier to climb a mouqd-moa v;l kgz: 0-ig6ntain via a zigzag trail than to climb straight upmq;v ozg 0d6k igl--:a?

Recall from Chapter 4, Example 4–14, that you 8z ap 0wp:jw/,,ylshxcan use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–3p wsj,/la:0y p x8z,wh4). 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 gravitatnoi 42yd+ sf:uional force when a 265-kg pile driver falls+n u :4diyof2s 2.80 m?    J

  A 65.0-kg firefighter climbs a flight kzd:4; t(j5g xwf,k miof stairs 20.0 m high. How much work is required? z,igm:kft 5xkd4w(j;   J

  A 1300-N crate rests on the floor. How much w f (tmp10.klmoork is required to move it at constant speed (a) 4.0 m opmlk1f t0.(m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers d, pil9zg)i4(o, iajnh tns,fe b+b.v:o (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of frictie :i4tflpvb b9, oj i,i)+gn n(az.,shon was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force */ay985ulvlmjk ym- j across a floor at a rate of for 7.0 s. Find the jm*- u 8l/jlyk9ym5avnet work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How u. n bmcoc)054fmyf n yy967m.hca3px much wumofcb6.hn7m4) f0 a3ycmx 9n p.c5yyork is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 cc cbd)zvg6 4dw-uiv28an be used to liff objects we might not otherwise be able to liff. cbvudidvz4c )-8g w62 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 fromgle/ :tybzk-0 accelerating by a man who is pushing back on it parallel to the inclin:g /-ey blzt0ke (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M anbtjsj./ec-n 0 acceleration of 0.10 g upt n-.cjj 0/besward.    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 axisuku vgwg, v/011iaq)h 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 x7,8*2tzvjwp p;vk ssalong the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move vpv;7sk8pzjxws ,*t 2 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 fqx4qx(b 4:we 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 molecule, with mass of /ylu z8r0 b,hkb,pp,aah vt/. $5.31\times10^{-26}$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 whatzkofd)k0l k.+ 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 stop a/; g41tb,7p+fp fvwto qapwrnv 2n o/*n 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 cm 2qe(:u6 zfmcu)3jutraveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is firea8 (xi: jrh9u ;6w6dgnr v4zded from a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm.8xjz9ehuad v(d; r :w6grni46 What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s movps* xh+ (x c fqe.a65agcmc/(ies a fielder’s glove backward 25 cm when the ball i*a 6h+c f /aci(p.eqx5xmc(gss 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 brg;c ,d/hpjet /aking distance b;je ,hdt cg//pe 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’ (d g+zzqo,we-s skid mark to beezo+ wgzqd (-, 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass ofd apdod.-+ak w*ah/va54o w2h 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 pitcher is about hd/ 4oaov+kw hw 5a2 aap*-.dd15 m.    N

  How high will a 1.85-0q,sjlkali ,,dr, p73*t lfax kg rock go if thrown straight up by someone who does 80.0 J ,,l qtj,3lparai*k7lfd,0xs of work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sing apm)s/eo-t/u-yc 1fc le cable. Detea yct -mcpo)/1/sef u-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 Hoyjbyyinymtu6z6 ckb 25x5.gi2- h6c )w much must this spring be stretched to store 25 J of potential en)k.56 i uic y66 bjg5m-tznyc2h2bxyyergy?    m

  A 7.0-kg monkey swings from one xuxp*-; cx+qn branch to another 1.2 m higher. What is the change in pote xu+nqxx -;p*cntial energy?    J

  By how much does the gravitational potential energy of a 64-knk osjpv ikmwg736pi5d 9v;-2aq r6 m+g pole vaulter change if his center of mass rises about 4.0 mmqa imjd;vsg 26p 5+6kvi9nop73 w-kr during the jump?    J

  A 1200-kg car rolling on a horizontal surface has spee. u9s*bbcxfee5-+)qjll)zm m d v = 65 km/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 )jbz5*s+mcl9q fub x ml-.ee) constant of the spring?    N/m

  A 1.60-m tall person .vwh 5kqjj5o g;0-grh*1l3wf.4sxnzol a+zalifts a 2.10-kg book from the ground so it is 2.20 m above the ground. What is 5.l*jq0h+a w. jv hz5wkrf3o agg1nszlo -;4xthe 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 4hvuphv rry(1u9j 7xz,4ei /cand climbs to the top of a 3300-m peak.hpjv /rzcuhrxv(i4u e ,4y917
(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 8x(cov*b(/qtw ff ls; 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 attached to the end of the spring, where will the end of the spring line cb8q;xlv (/ wfo*( sftup with the ruler marks?    cm

  Jane, looking for Tarzan,opsfq8sf/;; b 6 ko+ol 5qlcz;+n;lw g 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 k5os f; l pcnl/ +o6+;bsgq8;q;wz folswing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a friction,ntc,vya s-z .less 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given an)-hg zrhk(*i 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’*qa6pm20k2pr 9v ergl s kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift he rm0a2 6r2*pkegvlqp9r center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of aro2n4ih vovk-+ h.o ;uy,t 2xz platform with a speed of 5.0 uv,2h2.z4r vh n o-okxti+yo; 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 (igh0ewn 6kga(7bm0 )t vnnore its mass), whose spring stiffness constant is 950N/m is ab0wt 0h me gv6(n7ank)ttached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without frice u3mj;2/ oso r+go;ck/ka*v fvao(9gtion along the looped track shown in Fig. 6–39. If the block ism/sa*ocf a 9 ;/ ug2oko( jkor+e3v;gv 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 of a spring (spring stiffness constans 1rk ta+8xpyx9vpz 18t k), Fig. 6–40. Thxkt pzxs1y v89rp+18 ae block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She x 7eq+g a4ek wcj:3jn*d n)5vhis tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffn *ngn4khve7)+w:xc35aj qj deess 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 draggev4hi iz5x0a5fe* js;p d up to point 1 where it is released from rest. Assumi5hs fp5i vxiae 0z;*j4ng 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+n4cuqss l iws1r 4: x+i+4vdf 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 oa+ ric 5jh+dak5a2v 6qam9en+f 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 sek5h5iqar+an 6dc a++am9j2 vhould 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 ysc q8cb:16dkcycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite direcs5i 0 gk9x4omkd8i6 ;l1 jo8ywsyifd-tions, collide head-on and come to rest. How much thermal energy is produced in this coloj yw 0y9 li814idd6igk-5xsfok ;s8mlision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descend v6il jn*opp4;s a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermali l46; njpvo*p energy due to friction was generated in this process?    J

  A ski starts from rest and slidesu5pt1 ktks 0-9o,jlft 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 ground. 1agzw-qee 2/c
(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 ofgj/,mswa:8bq. szdeonk : w dmy,7 d27 2.0 m, and it bounces back to a height of 1.5 mj7 /zbg:,d2m.de 7s, ydq:nsm 8w wkao.
(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 co:8. cz*hbm. mzukn6rjsz- t6j nstant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coeffic 6*ch-n bsj .mur:k8 6mjz.zztient 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 wdx(vh9 *u)ufmy i3dij-n9 fb*ith 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 traveled is 45.b dh(x 9y* f* iu3mj9vfud)n-i0 m. $\approx$    m/s

  A skier traveling 12m/s reaches thdi)+nktf;ykc* q)a0 le 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 ho yf9rbjqcp8/, rizontal 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 beforejy / prq,c9bf8 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 very70 cywgsrr.q6chm :(a9 brjp6 light horizontal spring, Fig. 6–40. The block can slide along a table where the coeffi0 .9:q(6pb 6 s r7jawcryrgcmhcient 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 kg includ63g wnxz, oi9jing pilot) that was launched horizontally at 500km/h from a height of 3500 oxwg 9n j3z6i,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 lg0axn4ox9 fzqb zp7* .ift a 315-kg piano to a sixth-story window 16.0 07np .zx9 *bgaz4f oqxm above?    s

  If a car generates 18 hp when traveling at a steady 88km/h xxk gw7v*5a(go/ yzn3 what must be the average force exe3g 7(ov5*wzngxx a/k yrted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7-lf9/s ku lkxr3hla6r;beq8d-rt (,b .4 s. What is the average(dk- ll lrehr8aq sxb;9,b-6tk u 3/fr power delivered by the engine?$\approx$    hp

  (a) Show that one British horsepowerxtftjohn7d -c6+ b*k5$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-hours.” s- ch d 7s+25rgqff/jg3 pyw0b
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in bg0:xw,hid3ecg:x4m g o 8izlq/d5 v7 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 a co / qwdibh0le4v8:dg x: omiz3, 5c7ggxnstant 75km/h.    hp

  How much work can a 3ypomh 4-t 9xub) a4i2u.0-hp motor 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 thityapv1 ;;o lipvku4n9q; 5 +sms motion takes 1.5 s, whati;+ qk9tv;ovs p a 5mu;py4ln1 average power was developed?$\approx$    W

  A pump is to lift 18.0 bhvn8)vh2x3*qlcp a +kg of water per minute through a height of 3.60 m. What output rating (watts) should the pump motor have? pn 8a 2h )l*qvhvc3b+x   W

  During a workout, the football players at State U. ran up the stadium stairs ishnd7 ) )eh*t-jwb 6aan 66 s. The stairs are 140 m 7eb aa6 wsd-*)hn h)tjlong 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 clincp3 3 4yswkj+pu/ n7;ony6ptmb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 h djyqmha40s4 (p. How steep a hill can it climb at a constant speed of 75km/h d 44aqmsh(yj 0if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motoy uk 3k x03c3.cj)yolwr have to be able to drag a 310-kg box along a level floor at a speed 33cwol0kyu.c3kx )yj of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0jp8qzxo);tg 6 jtf;kq h5g26u $^{\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 biw 8ziw4;lkaxvq 2(cg,)ar 5 cuilt “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 elastic spring up to th(a5agzvk,ccir8w )w4 ;l iq2x at point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the gro+ qmq4( ,sg*zjdm/hzlsah26ound, and the remaining four shelves mg4h+qz qah/m*, sz o6sdjl2(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 floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1fce- jasr7;:if7omdq 6p1vx+ po 1n,x936 Olympics shows that his center of mass rose 1.1 m from launch point to the top j: o;p+, i 7fnx -xmpr d1fv1s7eocqa6of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track sx(hz5dziggln f 6:qqrv a 9in6 0;x)w,hown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radius r. v5flz:9xg;n0 qq( dah 6rwg zx6i ),ni
(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 aircrao z4.zlrjof //f8ff: vft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, fzv8ofj:. lf4 //rzfobut 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 fi/spngyc4zm-r l /; x(yxed (Fig. 6–43). /prg yys /xl(4nm;-c z
(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 l.3 kha9zpt)n)*d nhato the top of a 3700-m-high mountain. The climb is made in 5)a)h*n hplnk. a9t3dz.0 h starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 2v - yw5w bcv+vw,**qly1 ,k72kuygzul8 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 i +clb *68: m*3ni 1zxmlfwendkn California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power neecil*f w 6zm3+d8 n:* 1bemklxnded.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s anb201gvkm 08 kp)b8kqwto gfm(; k9qo hd falls vertically 81 m before striking the turbine blok8o(qkfpmtwgv b89g10 hk)bqk m0;2ades. 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 coa drhwvn8uw x*(q8a a *8+ngmlu;dj 6y3ster with a circular 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 miw(3dlv +rayhg8nq *w xj8m d8;*6unua nimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly iz.43e09vll k ku+rnwxnto work, how high could an 82-kg man climb a ladder if he wk n.z+9xk3lu le04wvr ere 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 an ,vrnzukw 8u 5/2u6kji,a4m kt an upward 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 compresses 0.6be9l oms7a ,ofo a(;+v0 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 scale read at its pea9 l7 mbsoo;ovf ,aea(+k?    N

  A 65-kg student runs at 5m/s grabs a +hgcc 6,q.o*o 7byk dqrope, and swings out over a lake (Fig. 6–45). He releases the rope w .*oy6ck g,ohqqbd c7+hen his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.w* lq-)sw wle v0ec,t30 m in 9.0 s. What minimum power output was used to accomplish this feat?w*sv elc 3e0 )wlw-qt,    W

  Some electric-power companies ua ,mslu3qfg;,/q1 cjuse water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in sua ,ufq;,gjc1m /ql3 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/ffs1 ec, xvd ,hpejjt-xv.30 k is cut in half. What is the spring stiffness constant for each of.,jhv pv 1xc0texje f /3f-d,s the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a r, ij ;y0n u-tskv7l3gcne km)5ough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long will i. * j6p :sle6aohuv7bvt take to accelerate j*o p7hv.vu:blaes6 6from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (theu go);psfj/ tdj6 ,6ih “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient whenios6h ,jt) ;ufgd6 j/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 spew nt 4o :c8p-l d.wlm a4)zzjksjlkl)5(s a 500-kg rock vertically upward a distance of 500 m, what was its velocity when it left tt.p8jkka(ll :w m ds5 4cl-)) 4ozjnlzhe 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 waterug8,o:g ): 6fqxrnsyv wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provfxynu:ggq6 , s:r8 )ovide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s