In what ways is the word “work” as used in everyday zndj(-xgf 3 s8language the same as that defined in physics? In what ways is 3f gj(dnz-s8x it different? Give examples of both.

Can a centripetal force ever do work ora3dkv o)x.g; n an object? Explain.

Can the normal force on an objec;5ajhz4z c-lf9uodruj6t . u:t ever do work? Explain.

A woman swimming upstream is notz n4-iv /mp-x/kg ue-fa(j 8zbjq** lc moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on heb*mfuzz legxpkj-48vic a*q( /-/n j-r?

Is the work done by kinetic frictio499uqnp a-u u -zkwj0on forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from 99pa onkjquu4-zu 0- wunder them.]

Why is it tiring to push hard against a solid wa) u 40wojxom8dll even though you are doing no o)jwm04xodu8 work?

You have two springs that are identical except that sprinsw.6j wx xq)b m+njt9e lan/iwj4,(n,g l is stiffer than sprian+w,(.)x 9j,jnwexlm6sn j w 4 btqi/ng 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 94fhdru zn mu4h4 j1 mi6qae3+horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts frf644nqud 9h r3mezj14mi+h a uom 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 muw ec:*qnt-j.d9 8 p1a 67gkz+mhujpozch does your gravitational potential energy change when youz8gd n9ehzj+m 7qp-.1u*6c :ok awtjp jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roofd.dvc y5c 88rxits6s+ of a building, all with the same speed but with different launch angles. Which one has the high+.iy658xtdrcs c d8vs est speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a heighfg,5 -k.r izzet 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 tg-, ze5z .kfrihe 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 spring bysv nehy o643q, pressing down with your hand and then release oyv q34h,sne6 it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wiret 7nb un1j:ra:ar*q;s (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 than::rj 1q n7s;tbu* are ball without pushing it. Why?

What happens to the gravitational potential en4 md)47j,rawrl-np ryergy when water at the top of a waterfall 4rjyd7l)a rpm, 4w nr-falls to the pool below?

Describe the energy n7s*fllao .qs4er4/ ktransformations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skiio88a.xam3 x adng down a hill, but after a time is brought to rest by striking a snow8 3 m8aoaa.xxddrift.

A child on a sled (total mass m) starts from rest at the top of v549tv b 7jhpkn2etr8 a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill 4n2vr58jp 79vetkthbif (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in dq,k-plwt k h-+(u odkd;01gdtheir path rather than stepping on top and jumping down on the ottl qkd -kddg,d+ (k0-p; uhw1oher side. Explain.

Two identical arrows, one with twice the spex4 kadpfuyzg+h(m:m s 2i1 8)led of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than thu1xzaf)4 mi+m hs(ykp l 2d8:ge slower arrow? Explain.

Analyze the motion of a simple swinging pendulum vhhx1m86b- ct in terms of energy, (a) ignoring friction, and (b) taking friction into-mhxbv1 h6 tc8 account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater thanf0jfd ckl g,uuhku12:4ba, a 5 its original heigh15u , jufa2bh ca0d ugk,lf4k:t? Explain.

Suppose you lift a suitcase from the floor to a table. The wo lel*12kwa1jlrk you do on the suitcase depends on which of the following: (a) whether you lift it straight up or a1el2 lalw j1k*long 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 powejo kb -c wb),da)/fs(kr needed rather than the work.

Why is it easier to climb a mountain via a z+tsa)6n4y nvr igzag trail than to climb straight uy +t4v6anr )nsp?

Recall from Chapter 4, Example 4–14, that you can use a pulley and rblnow* gf3jnyx87 -:j7(u+oo p h8 qkaopes to decrease the force needed to raise a heavy load (s7jxunl pnob yj8 8k(o-h:* g+w7fa 3oqee Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pilqfwx6j 2v q)6uwwa(:p e driver falls 2.:x uwpqj v6)w26q(faw 80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. bc.(7n hwnlb7yps7g1 How much work is required?.b1 7w(y lbgcpn7h7ns    J

  A 1300-N crate rests on the floor. How much work is required a/ini:ewuoak+d6t -+ 1ks) pa to move it at constant speed (a) 4.0 m along the floor against a friction for-a1 ts/kuioa:6in++kdw epa )ce of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the moversm.x3vdcghvc5p 2w ln;5d va :. do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without accele d5 :.;cpnvgdx5ac23vwlvh .mration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg wqb6rna0s; w: is accelerated by a force across a floor at a rate of for 7.0 s. Find the net work donew6 sqw:;r0n ab on the box.   J

  Eight books, each 4.3 cm tht*hjs-m9:z9o255hk kdzw *i ngr vd 5yick with mass 1.7 kg, lie flat on a table. How much work is required to stack them wm25 y5n 99:oh zk*dh-jrst gd*vi5zkone on top of another?    J

A lever such as that shown in Fig. 6-,.;drwgli c; o35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output forco ,;wdgcri;l.e, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from accelerating by5j ,kov4 :d;nnebu,lp a man who is pushing back on it parallel to the incline (Fig. 6obkj,; p,ed5 un4: vln-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 cvlz7 l5j lg6-an acceleration of 0.10 g upwarzj 6gl- 5clv7ld.    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 dismki l+oc;u+ m,.fweu-tance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fig.9jchotk)smra. p. ; jp6brp*, r*uvr 3 6–37. Determine the work done by this force to move the objecto*9 r m3; tj..prkpu 6cjh)*rbp ,vsra (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 the e9onniz.r z/8ru er6/ $+x$ 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, an4w7j6ip brg .8m1rs g9e0zg eq 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 w0)*e tuw)mt rchat 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 fi+ t9ocb 9xqcl7 a5krbfe:8) 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 t ll3)fu6k 8qgx-vq- hko stop a 1250-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 e6k5- os9 eg s5a wvwm7nt)o3daverage force of 110 N on the 93s5 ae5g eno w7)tvsmw-do6 karrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelicex4z+044 b :wbdskwlng 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on thec: xbw44 k0s ldze+4wb glove?    N

If the speed of a car is incrlxo); 6qr5 tls5c-d6*tpl7zn8dnqwz eased by 50%, by what factor will its minimum braking distance b; przso5qwdl6 t5l) t8nncldzq6 *x7 -e increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure 9mjg6qf w y08xa 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 6wgmx80y9j f qthe driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the ti7hf.)lq 03aurzh ca ,5i2oit cme 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 0 i2 quf7t,3a z )o5.lcrichahpitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by som/n +uk)le kq*lqkhxi8(o8e4z eone who does 80.0 J of work on it? Neglect air resisnx e iq4*+klk8kq oz(u/he8)ltance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single cs5sk 7p5w f6g 8;edho,+oe+o zx)sjmnable. Deonf s eos),j58egdxs7poz+wm +5 h6k;termine
(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 sprin*vfo-e qc x2o9g stiffness constant, k, of 440N/m How much must this spring be sfxo2ovc*qe9 -tretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch k, -gh *ztq/bov6zj;g flqw1;to another 1.2 m higher. What is the change in z/b ljkg;zfwv g1*6,;-qoqht potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter cha:eyceubv/xw r* :i ,:rnge if his center of mass rises abouiyvxu* e:re, wr::bc/t 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal sur;/2tyg t5li(jz b2sq xface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to resb 5sg j/ttzqi;22 yxl(t in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg xtrh u,vxj 65 kif,qo/)o,nz9book from the ground so it is 2.20 m above the ground. What is the potential e ,vithxquxk56 z rf9nj,) oo/,nergy 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 nhpwlz0k;h0+: jz bi0j* /mcitop of a 3300-m p:c0 0kh/n im*zi +wjz ;j0hbpleak.
(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 the sfb+d.l i+ nf.mpring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the ei++.b f .lfnmdnd of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vi x),+ hjwb6b:xn9-a nijh ozm(ne hanging vertically from a tall tree in the jungle. How high can sn9xzha(6hb +, : onbmjw-)ixjhe swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides dovg n 6yegapx.5;s.tt02 7urin wn 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 frictionless 28.p1c./22 qsajzog* 1l:do czar 0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformh0 *uzdz h *j/y:/ eis3fguvv5ed into gravitational potential energy without the aid of a pole. With3h v*ez jys*:5zgi/ 0vudh/ fu what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upwgjhq ml3fcz4)ou vst8 k 8bby2;)iq04ard from the top of a platform with a speed of 5.0f zkh4m)qj3b08lgu s b)y t o4v2i;q8c 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 c-qld9df u 5wh mcdmk* 1a1,qh9onstant is 950N/m is attached to a table 1q9dc fhdqmw,l-*1ua5mh9dkand 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 friction along the loo*c a2ag)bnl(jped track shown in Fig. 6–39. If the block is to remain on the track, eve an (ca2bj*)lgn 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 ti ,p a84xglvbn5i0:rv yq;g6ahe end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displaceme;6pg :r0i8 qvaixvn ayglb,4 5nt $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord wpi+m0t* lv w0mk)8hau4q4jtg mts 73pws0rf8 hose unstretched length is 12 m, and falls a totalpi um*34 m l70t8sa0w)wh sr vqgf8+tk4mp0 jt of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 where it is rsi4e 2 ms09jqo q)4 ko3w1ix huna7 6(8gvuysqew aq9y81isu(ohi4 62om eu7ns3q)v sxg jk04 qleased from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle.1sz5 l(-cy ip)yl fis 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 placea5n;tv o( *sxod at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengsvo(5o* ax nt;ers 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 togjiu+(-0yfsrnig.a 5 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, eac 4u -r nhm/y*.)hzmnw2ii um3ih of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal enerzym.w4ii3mu nnh-/2hru ) * imgy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m h28y0 r cwuw0:ugnynu3 igh and reaches the bottom with a speed of 2.2m/s How much thermal energ cw0 yu2uu8nwg30ny:r y due to friction was generated in this process?    J

  A ski starts from res 1c4llon9 nmxwy;y/i9( cqjv,t 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 y*7c- + y 3cnaml*ovy fjfwnjc8;r160lkcm;x a 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,*dtdnl.c 5w /i and it bounces back to a height of 1.5 m. /n .cdd*tlw5i
(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 amkg) hdqu18 ;k 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 0.30q; mdg)81kkhu. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes poitjainy* t -mji;3.u3ent 1 with a speed of If the ave*y 3je-uma; nt3itj.i rage force 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 18.0pfz iftkb:mvxs, ;* mq7-s 8u) $^{\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 attacvrk( h 7q+3rtnca3 pc b:5;wxmhed 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 the3rpmt h(3 +rw : xb7qn;5vckac block and the table?   

  A 280-g wood block is firmly attached to a very light hori s3yke0 1aota0zontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far bets 0oyk1a03a eyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the ,f 0d9h(k/npvh d(qgda5;mac space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h frdc, vad(;pkn 0ahf(qg h/59dmom 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 a 1750-W motor to lift a 315-kg piano to a sixt apg,z:vcoii 4o pe8h -uq ulwe6;d-27d5gb;k h-story window 16.0 m above? dgq;e:idbz7eip--gh klwua o,6p;c 5uvo428    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the avu1 6hqbg7sny*- (* p/ pucq(0skdy nqcerage force g(d(uq/0 n*kn-yp17q6h sccy ubq *spexerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accu.ki01q* fls q,a. 7grqrrog*elerates from rest to 95km/h in 7.4 s. What is the average power delivered by the enginelr0q,g 7 r*kgrq s oa*1ifqu..?$\approx$    hp

  (a) Show that one British hornj)ag)t2(b,z cgux/p 0h* syc sepower$ \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 theeto+ pq08b f:j4wqo4 8 uifp2c form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 11eg)y40ju 6ym(0jhnru 50-kg car slows down from to 65km/h in 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 connuhy4 (y0um6j0 egjr)stant 75km/h.    hp

  How much work can a 3.0-hp motcom x2*z4ck+7,ah uaw or do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motdu9 c4wgszbbf* 4 lk;7ion takes 1.5 s, what average power was 4 dzu7g9bf4cw;k sb* ldeveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through af6 6w tsol:qh6 height of 3.60 m. What output rato q6 w6flth:s6ing (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the st lf*n,g8mh o)radium stairs in 66 s. The stairs are 140 m lon)8rfg* o ml,nhg 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 climb a 6cj-ygt *cfv64n)( 55 ly tdyzl.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 hp. How steep a hill can it c( .0q9zuqnud v0p(tnslimb at a constant speqn dsu(q9ntz0pu (.v0ed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a b1 /a q 7-bnth1mssr z-id;ts7w1kxo*motor have to be able to drag a 310-kg box along a level floor atsqox1-mn/d 7rs hs1tb-a t w7 kiz;b*1 a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts d0)4q, pindhgjown a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that are designed togtj9,jp-f lf* 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 constg-9f, ftp ljj*ant 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 dryha1u;x1d2zpnr- n+ or+d-und, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg withny h ;rdor1pa rx1z-2n-u dd++ 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 Og( jg uaoqtsy9,u,r*2lympics shows that his center of mass rose 1.1 m from launch point to the o, ua 9rjgut2y*,(qsgtop of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the ewko: v-ap*/n looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radius re p-:vw*/na ko.
(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 withooz.sv +vccuz+4v48myut his parachute opening. He landed in a snowbank, creating a crater 1.1 m d4c48c+uzzv+vsmvy.o eep, 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 hoiwzqy2d7eioh 6; 4 myx *d(ze,rizontal cord of length L whose other end is fixed (Fig. ,*i 47(qeex6w h 2oymd;yzidz 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 climk -6 .qeszkg0ab is made in 5.0 h starting at an elevations-kke gq6.za0 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 whe6wz/gg; .dwe,w 2)svm)pbq6/erv gnin 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 areash diz:4/a90og5g nv,jh 2yzr in California claims that its lifts can move 47,000 people per hour. If the average liftiz sggh,vr/z5oy 9ja4h02: nd 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/ tubjj3:woj(s/ 6bo uoif, 0-gh5xmq9s and falls vertically 81 m before striking the turbine blades. Calculate gbjohwomu(:t 5jsbo f 906j-/,q3 ux i
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6– yg 0k .l/xn7szruguzuc+*.4w44), 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 need n* /rs..uxwluz7+c4 kyzu0 gged, 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 dirk4fxt,6.ijkmhxf d2tqfl,-u *k6bn,ectly into work, how high could an 82-kg man climb a ladder if he were fueled j m,nli 2f,*x 4x-kfkt 6qbh6d kuf,t.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 ondvg5012u q oxf 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 bat tr.v9-p8,jjg6kydt7 7 .rjq(pai d nrhroom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 - kqt8yar6tn.j .jrgp (dji79rd 7pv ,m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a:u eo)lfosd; pgq0f*4 lake (Fig. 6–45). He releases th : gd0)*lfp;o sefquo4e 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 distan+gjjvfd 8vfy;y7 w114 rhan6o ce of 5.0 m in 9.0 s. What minimum power output was used to accomplish 4f8n1f;1gda 6 jhj vvw +ry7oythis feat?    W

  Some electric-power companiek luwx d2+aag,ug4.sqd rx3f wz(aph8qs-.8:s use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the ene3x:(+ d8whzfau lr82usd.q4w g,qpxsg a.k a-rgy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant j83tb-akd . bbk is cut in half. What is the spring stiffness-aj3t kdb8bb. constant for each of the two resulting springs?   k

  A 6.0-kg block is push jky+ )(ghgxn8dg (q6ged 8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can r0adpl nq2:l+n9li/ak( gan/accelerate from 35km/h to 55km/h in 3.2 s, how long will it take to accean aadl/+ l2k l(9:gqn/i0rnplerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac6 :g ,xmfdi4u8gspve -pn4 mi6 function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when t6 m:i48 pfns eg- 6xug,dimvp4he treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock verticallyl 5xv ns45zz*e upward a distance of 500 m, what was its velocity when it len5xvs 4*zz e5lft 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 heigh vakn5ge ak944vg hp;0t of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, whag;gh9e4n4 ak5k 0pva vt is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s