In what ways is the word “work” as used in evy1ks qur s004ceryday language the same as that defined in physics? In what ways is ik q ys41cusr00t different? Give examples of both.

Can a centripetal force ever do work on an object? Exp k.c66 iwo;+oig-oidhlain.

Can the normal force on an object ever do work? E97b kbql .8njexplain.

A woman swimming upstream is not moving with respect to t2yj-ax 81jg krhe shore. Is she doing any work? If she stops swimming and merely floats, is work done on h-ay2xgr8 j kj1er?

Is the work done by kinetic friction forces always negative? [Hit/qi6c .t +gzant: Consider what happens to the dis .g+/tatqcz6ihes when you pull a tablecloth out from under them.]

Why is it tiring to pusch45 l aik65gph hard against a solid wall even though you are doing no wo5k6h5apg4 cil rk?

You have two springs th i4fb bs-9 -tt7yf3nyyat are identical except that spring l is stiffer than spring 27ybtnyb y9 3f-fti4s- $(k_1>k_2).$ 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 tpc/c0 c:+z yntj(d3z to slide on a frictionless3c/yjtdz ccnp zt(:+0 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 mz4i,:kwy z v; t3 aiw;11ai7rsb1wwfn uch does your gravitational potential energy change when you jump as higy:wvf7 bi3izt ;11s 1k;zwirn4, aww ah as you can?

In Fig. 6–31, water balloons zb2v+tu p51cdy4j34ip w ttc7are tossed from the roof of a building, all with the same speed but with diffejv453 zdpyb2 wutcpc1+tt7i4rent launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is c;xioq1;v i+v:1 az lwa height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium;1ovqzl 1 c+v:xwiia ; position? Explain.

A coil spring of mass m rests upright on a tabtma)x x.iity*sl8 56yu s07s 8bbfy1ule. If you compress the spring by pressing down with your hand and then release it, can the spring leave the ta7 )uauiit.5s8lf 0x 6bx*tbm 8y y1sysble? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by abmmvxn; ; 6*sp steel wire (Fig. 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 withmnvm *6sbp; ;xout pushing it. Why?

What happens to the gravitational potential energy when water at the top fvfhal/kyege i:kjwi2 r9ph. t- 21*1 of a waterfall falls to the pooe1./h1tr9jakf klf-i i e2wv2ghpy:*l below?

Describe the energy transformations when a child hj9tim; -qpq3(0ydpfj ops around on a pogo stick.

Describe the energy transformations that take place whenk:5 g 1mv99gad9hmcnltp+t l 1 a skier starts skiing down a hill, but after a time is brought to rest by strikingcpl1t+19navt 9gd k: lhm9m5 g a snowdrift.

A child on a sled (total mass m) starts from rest at the)/ mgtygskl/w*bb:p3 w)+ bpy top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b *gk +w y)/p3wgpy)ml bt/bb:s) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather than smiji av87 3wq8tepping j 83 i8i7vmaqwon top and jumping down on the other side. Explain.

Two identical arrows, one with twice throradm9n 6 h o,/7osvte)oi3old d+93 e speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional forcehoo39dv +m79 es/to ddl r6,a)ooi r3n 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, masio 9ud6ilfi;022 7( t3knczfu2v y(a) ignoring friction, and (b) taking friction into account. Explain why a grandfathers kzocnf( 2; tf u32viyi2a7 09l6idum clock has to be wound up.

When a “superball” is dropped, can it rebound to a height grem(b wd5-fyib-j tq53 l l:vjpx)x5cl2ater than its original height? q 2fi3w- x(-ylbp5:5vtxb jlj 5 cl)mdExplain.

Suppose you lift a suitcase from the floor to a table. The work you do on theu 05p l*imjoi.s6l nm5 suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the sl 6*iinm ol u55j0.mpweight of the suitcase?

Repeat Question 22 for the power41np3gbfbg8erk.y 8u needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to wypauwa 5551eclimb straight upwe55aa yuwp 15?

Recall from Chapter 4, Example 4–14, that you 6y6scmur70 uycan use a pulley and ropes to decrease the force needed 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 concepym7 66cyus u0rts.

  How much work is done by the gx 3;hwm;/rjcgravitational force when a 265-kg pile driver falls 2c ;w/hm3; gjxr.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0njppizk6, +b/ m high. How much work is requiredjpp/b,nz k+6 i?    J

  A 1300-N crate rests on the floor. How much work is required to move it at consto 1/x+r:bub mnant speed (a) 4.0 m along the floor against a frict mbx/1+ uor:bnion force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushi fpa,ah2 6wcf;lk7w8sng a 160-kg crate 10.3 m acrosswpak,l82fwfa76; h cs a rough floor without acceleration, if the effective 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 . o-p+wv )yqc(g5eo*at bjyh:of for 7.0 s. Find the net work doq- :ob*ga vy wh.cp)+te(oy5 jne on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on f-zn x sk*8h8za table. How much workxk-zf8h z8*ns is required to stack them one on top of another?    J

A lever such as that show9c wcl69o:wm w, 4lnjpn in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Sl, wcownwp j9m:49c6 lhow 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 acce2 sqmc6ht0pg: lerating by ac pms6gq:t20 h man who is pushing back on it parallel to the incline (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 helicoptelxl- i /twcmfhpv1;2 s7e vm98r of mass M an acceleration of 0.10 g upwa;mvpvmh8f s l2 t/exi 9c7wl1-rd.    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 linear*se:) rk7ur maty/t 5x and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fig. 6–37. nxtbc 6(t: f ae3dq420mslbi4y)r7jeDetermine the work done by this force to move the objectb4( )m7bsy 6intrfjdq0t3a:4 cxee 2l (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 onef2x2 ru,y; zh a 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 molqmxeqe x xien5 fmgt7.9cb5)c- v2h+) ecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has rl,mdn1dp,3-dr,itj 0 fgh4 eits 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 ajv.cjoxs8;o(0 34bhj8j pv pjn 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 1250qhpgn5w9) q*,s l0r aycdv 74n-kgcar traveling 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 f1-kqgv l21ok s v;rw sdfgmss2 x-s8+,orce of 110 N on thkf ;gkws1svlsr18x,q2sg o+ dsv2m-- e arrow over 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 m)-h3gb84ywc2lcb b (igyj +nq z .sqz(oves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted cgqc28wzj34yqs zly( bhb. +nb-ig) ( by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factlgoz(d qk)6+lor will its minimum braking distance be increased, assuming all else is thqz( 6dkl+og)l e same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigatorgp imf8;)3tnp wvz 0 lsv*pw./s 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 d8p0n w)v p;*3 /pw tlmgsfzi.vriver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 t js (pm+hjat- pmgxi20mpx6,x)vz6czo 3,.lkg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air res(x6m3a sjz-pp+z otlvx0,,mgx.)t 2imc6pj histance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown str (c8vbucrf 19+4 qfsfnaight up by someone who does 80.0 J of work on it? Neglect airf ffu91cn8sq4+cbr( v resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration 8 k2b*sz+fu)0vc4kmr/qczyo nkz6,b 3 c,ty n by a single cable. k,zcnt uv,z/sy qcc0k 46 ofkbm*z8+b3n )2yrDetermine
(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 Ho;qk i*pdg)2rhw cituw**v d- 5w much must this spring be stretched to store 25 J of potenti gwipihc*;v* tdqd)2uk* 5-rwal energy?    m

  A 7.0-kg monkey swings:xqtc+a; e5c*g.b6vtiep . yx from one branch to another 1.2 m higher. What is the change in potential enegc6 b5iv+.xa t.e:*y ctpe x;qrgy?    J

  By how much does the gravitational pote:(ny zc)evn8nntial energy of a 64-kg pole vaulter change if his center of mass rises about cz :8nnny(ve) 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when iq)ut3m4 jl +ght strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is th+ghtu 3l)j qm4e spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts (m1w bz)z(zhxa 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potentbw(z xz)hz(m1ial 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 a 3300u:jx ffbu/n0ei )b* p(t g;kuy8b.pv,-m peak. byi/bkb fnfj :*tp).ugvu; ,p8 (0uxe
(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 fx0u5+8 trqcc hangs vertically 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 nowtf +rucq 805cx attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) andk 53z ghp,o3r1j f-nl5cwz q0w grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward3ro p g lk wh3qznc,z1f55j0w-?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from r wtcw s 73heoo34;ioe8est, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frif96ov jhnjce 2vx42v7ctionless 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 ena nn+ xq5( 3f(oyyq,syergy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leavn(q3+as( 5qyf,yo n xye the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps verticall+v -b6:r/humjg v995 at4v fcu2nhkduy upward from the top of a platform with a speedv4+6df29j- / nakhug:v ubvt9mruh 5c 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;mr9hfn ew;*z its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to rw9;mfe zn*;ha 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 frictioufh l5u,m18uf-jgl8c n along 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 minimum height h mustjcf,hm8 uf8ullu 5 -g1 it be released?    r

A block of mass m is attached to the end of a spring (springl hr-j ;vv/r36i9w)axtb3s hzb hi 8:m stiffness constant k), Fig. 6–40. The block is given anv/l6:3-aw hmbbi ;3izx8h9rt ) hvrjs 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. S7c 8fb.x g9lgpa h/x+iv50msq he is tied to a bungee cord whose unstretche5xhsm80p qgf+glax . ic79b v/d length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is4u;*6.kkgwpgj/ez ;i miq b:g dragged up to point 1 where it is released from rest. Assuming no friction, cak4*e jgbkw i zm;:quip6g. g;/lculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is th4/ 3qpxkbp u1trown with a speed 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 the bottom of an 45sbx22xmv u4*ztjvn 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 s s *zxj2xv 54vtnbmu42hould 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 (dk zl.r5s2ewz q:9wr cycle 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 o,k990nnddliq5v a (a il w+c(npposite directions, collide head-on and come to rest. Hod vk (nn9wca qna5+di,l90il (w much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m hi )acl n*+1ixtsgh and reaches the bottom with a speed of 2.2m/s How ms+nt)ai lx* 1cuch thermal energy due to friction was generated in this process?    J

  A ski starts from restp;b0h(x 73vh51sqfttfxm q (r 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 ay hkn9kg(57cfi/( gxk tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it; zfkbs+tr wn5.1o.jdv1zmd* bounces back to a height of 1.5 m. f1n5t .m*+ kwdo;s z1brvdzj.
(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 f395lhknb e adtk(es0:loor 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 fris5 ee0th a3nl:(dkb 9kction 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 iky1lw (*/c 8 w)ykwagof If the average force of frict/8kwwyyk 1ca *)glw( iion 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 wmlrdun)5/3a2*,uau-74 vngo cn fqssteady 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+xxc5 m0h;ixr *dj5 fq is firmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and thexjmcx5rh 5x ;+ d*f0iq table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, rhry ;.,oytxo 4yld14Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium poy.o,lyyr4 4xdhr1;tosition will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg incmgdxf/v/j+(wrz g75 d; qot/cluding pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed tqgjd/gc z7;r d5f //o+(xvwm of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-story winvntjv a8uc/2 0zk c9(ldow 16.0 m a kz/a j9(cvlu8ctv0 2nbove?    s

  If a car generates 18 hp whe3,mmf/g w e;t/tu9uv2k *ejl tn traveling at a steady 88km/h what must be the average force exerted on the carfmu vk2 /t,9 tmel;u3wje gt*/ due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is ths0ff.mb8ym , 8r (ttloe average power delivered 0os.ytfb t8 ,frl8 (mmby the engine?$\approx$    hp

  (a) Show that one British h:u *keouc2sxs7k(j(e orsepower$ \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.” ;-bj ai.hj6 lj
(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-kd i7z;k);v euyg car slows down from to 65km/h in about 6.0 s on the level when it is kdevy; 7;zui)in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0g1seu atby+ 04-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from .na64zozivvj n/ jqf(,mo32krest to 14m/s If this motion takes 6 jv4( k.fzo,/mjninv2qo za31.5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute throe :eg)t5kgb q1ugh a height of 3.60 m. What outp qg5teke1:b)gut rating (watts) should the pump motor have?    W

  During a workout, the football players at Sta0 :5ru52 ,va m f7fkjww(brgwdte U. ran up the stadium stairs in 66 s. Thewmgvuff2: bw(kr5djaw 5 ,7r 0 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 clim uq4hlsl8g r+z3md a,em(z:3 ub 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 outpu:m57 c 6zj go ard azy7uox;m2;w9kpa*t of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the fr acmmd9pax k jow7:7zr;*;5z 2gu6 oyaictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a mo.g6/:yulx jzrzh1v, ytor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficiz y1/vh.:x yrgj,l z6uent of friction is 0.45?    hp

  A bicyclist coasts down a 7. 0/skhc(-at/*ftjqn.mu4ahli v f 9*u0 $^{\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 haq. mpd;kq 41cmve 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 point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 km; k1pq 4qc.dmg 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,97qjxrr *)a fvbnc 79t and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average bo)rf7 v x7rq bnc9t9j*aok 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 (m qo h n*425zxenn.t5;f,xc ogw:ttg: Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at th:qxmt t ,:gfo5wx4ntc5 .ehnzong*2;e top of the arc?   m/s

  The block of mass m sliding without friction along the looped tkj ly4vo2)g+aj hd4*m r5ys4 mc .a(ldimh83 vrack shown in Fig. 6–39 is to remain on the track at all times, ehl5*ayvmgdo8j23.+vl( yrm mja44i4kc hd)s ven 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 felyrx)xvwany/ tg,36ji/ z p2j,l 370 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg an,r6txza j 3i//)y j v2nywp,xgd 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 o l, 9.) 3,txigxmf t;ogwrmz:gf length L whose other end is fixed (Fi, xmt,rgif;wl 9xm:. ogzg)t3g. 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-high mountain. The climb is made in d:.s qhtk u)7ur;l lh15.0 h starting at an elev;sh1) u.k7 qll drhu:tation 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 92be8vff8 dks 2,0-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 Califo sqenaa:l+ ;v1 fz2g3er)3xvp rnia claims that its lifts can move 47,000 people per hour. If the aveeg n:3+)x az21l;arsfvqep v3 rage lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically f,ij z;cu6c a5 s8ep:u81 m before striking the turbine af6 pji zsucc u5;,8:eblades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circula7q2h rhsd* rz+r vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through h*+q z2d7hr srit.    mg

  (a) If the human body could convert a candy bar dirwr wbge2- by/0ectly into work, how high could an 82-kg man climb a ladder2 bgw/0bye-w r if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of -rli8qb:;mm8h t vrv 79**)yttzjdl p45.0$^{\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 sca02otu5cf; bm9atww o..lz ek17q-lh lle compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at itsl to59l70wqmu-kebfalc; zt h.w21.o peak?    N

  A 65-kg student runs at 5m-.95 6j .ry: qkxjfw+qgxut,sngs mm5/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his vel9q xjxw:5 yk5mmq,6gt.sjurn+ .gfs- ocity 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 v(+ v7gnjn 3bbwertical distance of 5.0 m in 9.0 s. What minimum power output ( 3g+jn7 nvbwbwas used to accomplish this feat?    W

  Some electric-power comphsc 9 8r0l/7okuttp)tanies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy prod/ 7 h)r9so8tkttc0pul uced 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. Whal-sp(efl0pe3wq3 y;g u cl4q6t is the spring stiffness constant for each of the two resultiul f-pe(g3p6yw0clqeq s4 ;l3ng springs?   k

  A 6.0-kg block is pushed 8.0 m up a ror0kw)x2.cjd wkghr 8pi :qc 68ugh 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/ ,o5t,k0lalu6rdd v.dn4 almda ab .:, how long will it take to accelerate from ,5ta :.4al dn 0/avu mldbrk,la dod6.55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “str o6b 8-.wuk8hjm)ji y2l9qgmkess test”), the patient walks 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 mj l)uw.k6k-m8i8g92h jobyq 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 v vbu)i 4vs4 8x2p(fewww-c.jgertically upward a distance of 500 m, what b-4swp.) jiu42 (w8fvgcx vewwas its velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 wak-og-)2f gw wtu*jt3bv2z 3m at a rate of 95kg/s (a) If 23 3jt )gbw*v wogztk -2ufa-wthis water wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s