In what ways is the word “work” as used in everyday language yd*p-n, *, ap kcu/lptthe same as that defined in physics? I*py ut-p, ,d/pc lk*nan what ways is it different? Give examples of both.

Can a centripetal force ever do work on.,sk 0d qmhl-f an object? Explain.

Can the normal force on an object ever do workulmj1 awb4,2k ? Explain.

A woman swimming upstream is not moving with respect to the shore. ,7azqu t (ys:nIs she doing any work? If she stops swimming and mere,u( y7:zasntqly floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: e3*)ho c lrxp4Consider what happens to the dishes when you pull a tablecllx )rc*4op h3eoth out from under them.]

Why is it tiring to push8 gw(/:atfeec x evx6pg2;v/ o hard against a solid wall even though you are doing no wofc :6gex2e tgwa/vvex /p;8o (rk?

You have two springs that are identical except that spring l is stiffer th mah9fqc/ jron8/rmae )h1y5 ub/nd- 3an spr/o e ym)9r8/fbn5 dr-c1qjahmn3ua /h ing 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to slide on a bt/umqiovojlr()(7: frictionless surface (Fig.6-30). The block starts)(m luj (bq/tr:vo oi7 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 change wvhd7 .91py6j/a fwa fghen you jump as high asfva.y/7fg ha dw69j1 p you can?

In Fig. 6–31, water balloons are eq2h,8uay.f 6 ivxzzb:b8;pj tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest s ,6u fjq.z2evxb8h y:8bziap ;peed on impact? Ignore air resistance.

A pendulum is launched from a point that is a h;n p2hls,q5lx eight 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 hxsn;5, 2 plqlOn the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the d)fo pecw (88qspring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the lawqwe8 p8cfo)(d of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (F oy gkc0)e45wkig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instc 4koegy0w)5kructor is supposed to release the ball without pushing it. Why?

What happens to the 2(y8qy(e4odrc w aa.dgravitational potential energy when water at the top of a waterfall falda2y(.ro4ycw8(q de als to the pool below?

Describe the energy tr)i7upz4 h.fh qvev-/ wansformations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skiing b8 t03dhi,1iha nxg;7 :aaz7s6 lap fsdown a hill, but after a time is brought to rest by striking p1 68zi7;ia :aa0nlfas37 bs gxdh ,tha snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of +13a) orabdrna7vl 5- cgk3nr height h and slides down. Does the velocity at the bottom depend on the angle of the hill if 7d- blc+3aar3gv )r1rannok5 (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step ovemg lm7o.x7p mek-4a4kr a fallen log in their path rather than stepping on top and jumping down on the other side. Explain7.ek7 kmxp ag4lm4m-o .

Two identical arrows, one with twice the speed of the other, are fired l 2xcfjt*m e8 f2w;-wcinto a bale of hay. Assuming the hay exerts a constant frictional e2c tw-c;*xmf2 8jlfw 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 of energy, (a) ign0wg9+lb *eiq ooring fricwq +b 9l*og0ietion, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it revb u5 o:gx-o fvvsy-,5bound to a height greater than its original height? Exof- :gyx,5 5uvbo-svv plain.

Suppose you lift a suitcase frtfik)-7 p 1es- yh*pkpom the floor to a table. The work you do on the suitca-f *-pkh)pe 7kt1pyis se depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for tqb7hs 1wq+cj/ e/e -c*l, xsdfhe power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb *zv,pjyn,+se 5iwj(g:zh, 0n njmpv8straight upnjzn,g0 8p ,+z( nejv 5hymwj:si,*pv ?

Recall from Chapter 4, Example 4–14, that you can use a puld nxnm o:0(y0bwsnnx ;qa4+y8 ley and ropes to decrease the force neq 48ns:x nyyn+ a0xmond0(b ;weded to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by thed tn oz.ak /)fmvk61(e gravitational force when a 265-kg pile driver fallsek )/. k6a1d(vmnfzt o 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How muchfp*cb/74 gehl work is reqb/ gcp74*elfh uired?    J

  A 1300-N crate rests on the floor. How much work n -dv 8aqu8)/r4pmftx is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 230 N, 8q4dnr v8ut /mfpa- x)   J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushingkxe d -,)p20:c,6c lpixkceam a 160-kg crate 10.3 m across a rough floor without acceleration, if the effect 6cec2 p p-ix0 lmkec),,dkax:ive coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of f.mmph sq:z8fb861cs;hq*pw oor 7.0 s. Find t8mq s8w; qmc: *b1 6hfphso.pzhe net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kbtu829nc::pt/zs:kaw xjl. a g, lie flat on a table. How much work is required to stack them one on top ofa:x /pu ka :s:t.2wnjb8tzcl9 another?    J

A lever such as that shown in Fig. 6-foi jb0x 88t 9,eujq-q35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output force, fxbj8tuq, 8e o0qi-j 9$F_{\mathrm{O}}$, 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 mood,trr53p/ye 8 -qp a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is t5,epm qod-3rpy 8/or0.40. 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 sa:esj w+ dn1/(j7 sava helicopter of mass M an acceleration of 0.10 g snj7 1 wda/ss+(vj: aeupward.    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 zt(e9htq:-nm7 vbd (zro 3bmjg h)* rr4r7.r mlinear 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 a u76+y vpc-jk,xitbrpn )y-,ys shown in Fig. 6–37. Determine the work done by this force to m,yk +r)u,cpy7 jynbv p6xti--ove the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts in e,ovwl)ay f8w38ux- q 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,/waph4ees 7 tvy3+(0ad e/pru an oxygen molecule, 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 -skk us7c 2av9hf*n.jzp ,p/v 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 requieqgqdf(6 *fj4tl9.6+eb c ni rred to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar tragl3f :5w4frv2t ly t1bveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average fonuk cvle6 z-54mxubd6q9- gd0rce of 110 N on the arrow 9ucn eddl-bz0 mu 5g6q-v6xk 4over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fiei89b. gj- bv* ;kjvjdklder’s glove backward 25 cm when the ball is caught. What j g *.j89k-;ibbjd vvkwas the average force exerted by the ball on the glove?    N

If the speed of a car is increasedv2i1-jnl dii 4.hp.de by 50%, by what factor will its minimum braking distance be increased, assum .-hivpn12lj.diied 4ing all else is the same? Ignore the driver’s reaction time.

  At an accident scene o8b,v)n1 h)gk jhkw+gcj d5 ng0n a level road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not mdnwjc)8+gnjk 5v,h 0kb1gh) g atter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it rb 1qz4(qkmksmb- *,vweaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance bevwqq mms4( b* k1bz-,ktween the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by some;8c.kfp.jm 2qw zl/ qqone who does 80.0 J of work on it? Neglect air qz mp8 2qqfjwc;/k..l resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sin1sgy4 eh z-5g .9xd)t1 noorze0zg.hdgle cable. Dzg0 o 1dznr.gzhyeeg 15-)x4d thso.9etermine
(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 must p a rzwv.8d/h70rr 8etthis spring be stretched to store 25 J of a r.r/08tw7rdphe zv8 potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the8tu od5ess y5+ change in potential enyeos5u+s 8d t5ergy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter :gy ac9x:yjp,u 4xm-oz (fc*xchange if his center of mass u o yga-mzx9pj ,*xcf:c4 y(:xrises about 4.0 m during the jump?    J

  A 1200-kg car rolling on op 5o+;tt 6mfya horizontal surface has speed 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 constant f+ t5y;ot opm6of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.h3z ghl- i9/wi20 m above the ground.-h9 w i3igl/zh What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts5wddcmt*4 e b5 at an elevation of 1600 m and climbs to the top of a 3300-m peak. mec5dwb45d*t
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of ulb(z+ioii(0 a6 :m zmge9(pfthe spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end oi m 6fbep(+ izl:(0gumazi9o( f 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 g k0 6fs +jcp,:+52hycc fseig:+t ivdkrabs a vine hanging vertically from a tall tree in c2,f5cgdi+tj ksf:y0v i:hs k+e 6p +cthe 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 from rest, slides down a frictionless 35 hy8 b,l/bchf b5-mthd3*4ra/cn0kn i.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionlmz mv(qvrk56( ess 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 ej05haer2- 1tv0h ucr .jtb 5qjnergy 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-1b c5jhrjt 0q j5urt2eh0 v.a bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platfor:nlv0h8p5e /5odi7ds,bb w-5 3xl qqnipmnl: m with nbqln580el w5 bs-l5i7q : vm/io: hdxpn,pd3a 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 spring stiffness constant is 950N/:o78xpw: 8 ,mfmzoo ijm is attached to a table and is compressed dowfo : pzx88o7m:wm,ijon 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 friction al iaw7*:6z e yfyrim(6fong the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what mm7 *ir wf:f 66(yayeizinimum height h must it be released?    r

A block of mass m is attay-o 6)qxm p(l dwatm+.s1i. aached to the end of a spring (spring stiffness constant k), Fig.6w 1.o+-sp.taa xmiqd mly)a( 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps/ (gole 3eea)q from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of)ogeq el e3(/a 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 i6qxf)t)t r*e 9bmul,k+ c7aeshown in Fig. 6–41 is dragged up to point 1 where it is released fr tt6)mclf+u,7q9 keb) ie* xarom 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 o m8q,kz+uc vlpm)ca-(hh. +p8dg 1czbf 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an gvlno-ndy m+o-d, 3 :qelevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, og-+yvnq, ndl-: dm 3ocalculate 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.

  A cyclist intends to cs4e m kts q7-y)bp6xtx6df 2x:x7ge9cycle 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 bnw8d s :)xf;buja/je y.eio9f99 r8atraveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this colson 9y xj: bd9/8ef awrf8jeu9ai.b;)lision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descetew1wd m50 i/hmw5p q;nds a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal enert5 hwp10ew 5;dmq/mwigy due to friction was generated in this process?    J

  A ski starts from rest and slides d vbbb *wx:dc+hd8tw:9o a.pl0own 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 g fx*;vbn 9b+ecjar; (tround.
(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 bounces back to a height of 1.57r- tvl:383 z5hmvxi sx9fe i ll2xgx( m lt 75ivg(m:2ll xx33zvxi9-xfrh s8e.
(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)ne2 *feqco*z ross 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 of the crat*)zec2n*eq o fe?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 witzqdv m.dux ld .u:+j5 9yr )l1,swwd3ph a speed of If the average force1rwz:vd 9u,.+ydpdl. j)q5sdxlwm3u of friction is equal to one-fifth of its weight, with what speed will 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 (4+*qln wn yyvv7 dys,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 firmlxl6y h) +v;(qt7le msfy 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, se ft)x6yhl lms+(7q ;vtretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached t co1 bjztk9w;.o a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A fot bz .1kw9c;jorce 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 useunq(7):3w,- mgft iltluoo j/d a “glider” (mass of 980 kg including pilot) that was l,7 w(l nmfqt:-t)3l gioujou/aunched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take 6/hl,xz 9hyla m*(q,h e y 0+lcejxv/ta 1750-W motor to lift a 315-kg piano to a sixth-story window 16.0 m a0j9t6l/ayxhvh + xyme (ce,hll zq* /,bove?    s

  If a car generates 18 hp when travelinhct042 oc.mcm g at a steady 88km/h what must be the average fortm. c02m4o chcce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h inb ryfg8 d:a2o, 7.4 s. What is the average power delivered by the engin:ra8fdb , o2yge?$\approx$    hp

  (a) Show that one British horsklq irrd/: 5i6epower$ \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.”6-qvqp,b b- h/fcvo)t
(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 doj0 n-+lcol tffq5-q1dwn from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately t5n+ lfldfqq1-c -j0owhat 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 motor9j ,hkf7 bv/my do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg q2k6ugktgz;.iub / odx0u *l,shot from rest to 14m/s If this motion takes 1.5 s, what okgt;lkg6 xu 2dzi .*0,b/uuqaverage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per gmoy bik2 b27v.6vy2b minute through a height of 3.60 m. What output rating (watts) should the pump motor have? kb222b6. m oyv7i byvg   W

  During a workout, the footbal)hbx k f,e5dpy(m ;w,dl players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and incl,fby(, x p);edk5mwdh ined 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 cl7 ::nips00mxp2;/zwjbzhi pd imb 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 maxi/;zz 8kuyab(f dt45dkmum power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to (4by5u/ ; afz t8kdkdz650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to 6zck 8ph1b7k vsl(9gh,tn8c*zdco 3 n drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is pd8 1scnk 3 lt,zcbghch6*zon8 (7 k9v0.45?    hp

  A bicyclist coasts dowid w-+fy-iaem -b60 jcn 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 carsplw 29pr4jz 8s:s3 iqt 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 elastic spring up to that p ps:r3 4sqji8zl9w2ptoint, 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 ground, anz)v-lx bh+ e;0d rai)nd the remaining four shelves are each spaced 30.0 cm above the previor ld;0)aih-n)+ xbvze us 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 Olympics sqp,l,8 6vg.buvc a b0+ :-rwg hoxii+ehows 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 of the0ei-vr,8qhwxb go+:,. lg bia vu+c 6p arc?   m/s

  The block of mass m sliding without friction along the looped traf/bf-gutot )kfag p9jm+l,a3e8y12 r ck shown in Fig. 6–39 is to remain on the track at all times, even at the ver jpfg8auytk )ffto- ,1ar/3 2mbgl+9ey top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft withwfpu)x tv 8 ck,gb-l87out his parachute opening. He landed in a snowbank, creating a crater 1.1 m deeb7,k)f8xcup - 8vgwl tp, 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 h)vzf:)om ef03on r :vzorizontal cord of length L whose other end is fixed (Fi ov nz)f3:f0:vomer)zg. 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-hig xj6nb+-*d6s ep6qcgq h mountain. The climb is made in 5.6-nxdq +se6*j gc 6pqb0 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 when393sv zn4q 6gnf -st.dwcapa ; 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 se3.0h-qmv/gz jh jm d24yv*lthat its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically0/32e-yjv4mhhmzq *d .gjs l v) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s andbh8a *ld p*t7c falls vertically 81 m before striking the turbine blades. Calculatech*at8p l b7d*
(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 verticd hy x7xmd-k-1h,bvc ps6.zc x4 g,g)tal loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of t-64v, y , gzpxh)cb7k.tgx-d xc1hms dhe circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, how high co s,5/o:hq8tp)ba h az3d2h hhquld an 82-kg man climb a ladder if he were fueled by one bar (=1t qh 5ha,aq:hh2o) b3/8 dzpsh000kJ)    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 upwawy9w8l. edk q)rd 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 bathroom2sipgq.zpa0 thk8;c. scale, the spring inside the scale compresses 0.60 mm, and it tells you yourp sa.cki 0.gtqp; 2z8h 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 peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings outwm7i2 lzep. el+h *e6u oxo1,:zw+ nsp over a lake (Fig. 6–45). He rele.xewh l+smin7woz*e 2ue 1o+z:p,lp6ases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical dizl4zs:5esc gqxl*h- * stance of 5.0 m in 9.0 s. Whalg 4x:*z*z sqlehcs5-t minimum power output was used to accomplish this feat?    W

  Some electric-power companies use wl880gi vkhl;v ater to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hog 0i8lvhv l;k8ur 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 st k7 :s xaxv sskhr)s-:d/.qk:32 gknatiffness constant k is cut in half. What is the spring stiffness constant for each of the two res/t : s2x7kxk-.nkds)vk:rqg3sh:sa aulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rou15vzt m3; )gnhavpqa7gh 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/hyrg(g(vc1b6 f0 el z8ph) 5ewp to 55km/h in 3.2 s, how long will it take toz8(bpcl 6 5vey)1grp( 0whgef accelerate 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 test”), the patient wa;be,rzy cl6d4 z 1)xvdl q-f)nlks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 1y lvdx) ;e),zqd n1cz6b-4lfr5 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a 3m8iydb q(rix (j *qf4distance of 500 m, what was its velocity when it left the volcano*83 mb(i( f4qijxqyd r? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s cycx+9xrah nu54n08m (a) If this w 4+uxcnray59nmh0x c8ater wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s