In what ways is the word “wo5e4m oxamv 2t -wm7df5tv);/p4gg wburk” as used in everyday language the same as that defined in phy/4 2o -ggb7;et m5pfud)atwm4mv5v wxsics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an ob-uc0g/ ;orm qpject? Explain.

Can the normal force on an o*c.w+e 5nmsqo s5:g* ps: g(f7gfcupobject ever do work? Explain.

A woman swimming upstream is not moving with respect ;6oqftnys 3 ,9i liygk9+ z jpcxsb70*to the shore. Is she doing any work? If she stops swimming and merely floatsp6j9c t iby,3+ozis f *s x;ln7gkyq09, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Cor0/dulj, 4h 2arwz0xg c8*awinsider what happens to the dis r2jxw*uawi,c l z r4g/0a0dh8hes when you pull a tablecloth out from under them.]

Why is it tiring to push hard againstst1y1ol: uvv 9 a solid wall even though you are doing no woruv91tlys:o 1v k?

You have two springs that are identical except that spring l is stiffergx-d*j iujo9kk(a a 5- than spring 2ja-kxg5k u a* ji9(d-o $(k_1>k_2).$ 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 freyubf :s2n4l4de to slide on a frictionless surface (Fi24u f4nyd:bl sg.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 much9r rqbkzk) )usp6gt*i k()( ni does your gravitational potential energy change when you jump as high as youkb)z9nrut q(i6 () ps ikrg)*k can?

In Fig. 6–31, water balloons a y1pw rm76lri6o-y1i xre tossed from the roof of a building, all with the same spi 71 1yprx-iyr6woml 6eed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a3*ffgpue9r;g o+y96 im4 tbyv 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,4v+yg;fm93y pbf oi9*r u 6egt 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 od 4yy9nh0 cs6mn a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of eny9y 0d4nsm6h cergy.

A bowling ball is hung from the ceiling byow)7a/w -8itukz8oc l a 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 suua-8 wlk/)7o8z otc wipposed to release the ball without pushing it. Why?

What happens to the gravitational poten7)as6 wsv y 0to-4cbcktial energy when water at the top of a waterfall falls to the pool below76 4yctsoks c)0bva- w?

Describe the energy transformations when a child hops arounjhff+ska. 8r 5d on a pogo stick.

Describe the energy transformations that take place when a skier starts skiing f8zl xs:)s:qd dr5rmr:xgr q,/2f0 sodown a hill, but afteosd/ f sd) 05:rq,qs:flrrxxr:2gm8zr a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top o3:d aa5oa gd1pf 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 3:op5gaa 1dad is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log i /zqg s6j8ho+mn their path rather than stepping on top and jumping down 6 h8g+m/zsj oqon the other side. Explain.

Two identical arrows, one with twice the dzq* c(cu wmmi,)k+7wge7hl(n fw (u+ speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow g7)(cwemcf7quu n+li(d kw * z(+h,mw will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum 7-ce3p(n /nw jp2vdpnin terms of energy, (a) ignoring friction, and (b) taking friction into account. Expl pn3nc(ev-n72 j pdw/pain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than im 6 649p 9zvh4 ;nqxwvhe9iqso *ploc;ts original height? Exniw4 o 4psm9* h; x9l;peqh z9ov6v6cqplain.

Suppose you lift a suitcase from the floor to a table. The work you do on w+t;.d g7 iw xtb+ 7kr3tixxr5the 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)ir.rig ;3xw7xbtw5t k x+d 7t+ the weight of the suitcase?

Repeat Question 22 for the power needed ral41q( :nqakcruvj hng+7u,3 n ther than the work.

Why is it easier to climb a mountain via a zigzag trail than to cmsh48vnhy. (hih9 .l tlimb straight up?nlmts9 hh (ih84.hy.v

Recall from Chapter 4, Example 4–14, that you can use a pulley lpyect2anmi1*69 +xta tfa82and ropes to decrease the 1l29y*a 6tte8xpni2 +aa tmfc 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 concepts.

  How much work is done by the gravitational force whzs* u b/7f9amhen a 265-kg pile driver falls 7 mbh*9suz /af2.80 m?    J

  A 65.0-kg firefighter climbs a fligh* za zk:pb,o q*dqi-x2t of stairs 20.0 m high. How much work is requi:kd*b* iz q -oq2azp,xred?    J

  A 1300-N crate rests on the fr-hi-;td/to2.eh tpkd h5 l i-loor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 230 N, .it; rkd/2-d -eth-5h otphli    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushinti) +d 6/imhshvb,2.sa/ pe jbg a 160-kg crate 10.3 m across a rough floor without am+bh.ih,)/a ivb6ps t/s2dj ecceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg onper 4d7;1qixrb2q78 e4dlj is accelerated by a force across a floor at a rate of for 7.0 s. Fie77j84rrpb4 lxi2odn d1qe;qnd the net work done on the box.   J

  Eight books, each 4.3 cm thiy1lin du 4ia1;k s*wk-ck with mass 1.7 kg, lie flat on a table. How much work is required to stack them one on top of anod*i yiakkn s1;w 41ul-ther?    J

A lever such as that shown in Fig. 6-3a7v2 t+m;5m ctqzrb8a 5 can be used to liff objects we might not otherwise be able to liff. Show that the ratio oftc b8rvza mma; 7t52+q 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 acceleratin;espj +ebzv2duf .t37f h x2s7g by aeh f7 s;v.ze 72s 23ujxt+bpfd 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 helicopj3 bu1eg+4vts ter of mass M an acceleration of 0. svj+te3b4g1u10 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is line8yo 8v sror6-3ulo *azar 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 objectkca. gjtu (j01, acting along the x axis, varies as shown in Fig. 6–37. Determin0j ut1g ka(c.je the work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particlh za7/d(cw.s)h2+ usrnas) bwe 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 oxi baw/7m /th.:ate -kxygen 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 a;dn h6br6:ashrrow is doubled, by what 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 t lua 1x7ysyd, 5f5j1dao 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-n w8gmz 6.1u+1g +npqdm e2krvkgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose sn.dt ua5zca2n :0.bq2 cjpa6dtring exerts an average force of 110 N on the arrow over a distanu5ac:a2z t da jpn.06q.2 cbdnce of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s mo2 r7mh:xovj5 6o -c rft*hn:o xmzz,c4ves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the bajorzfocmtm 5z:2v4 *x7,r:-hx h 6 oncll on the glove?    N

If the speed of a car is increased by 50%, by whatah ,s+z knowrq 0pis+-b-h b2mp3c4k2 factor will its minimum braking distance be increased, assuming all else is the same? Ign,+o-s km0nb232zac-p 4ir bq+hwphs k ore the driver’s reaction time.

  At an accident scene on a level road, investigators zb-) fv7 fful3measure 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 th) z7fbu f-lvf3e car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at +v vm qc+p 2+.d587mnik5ntw,h amefzBy the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the dist.t5+5 pz7+2mvemm+chqn n v, kiw8fda ance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someo3sf4,mw..kk qzm ru v-ne who does 80.0 J of wo4 -mw. svm .kqfuk,z3rrk on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m2 9d+w lcrrl;l 1:zeaa vertically with an acceleration by a single cable. Der9calr 1l+ldz2 a;e :wtermine
(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 4/ et);2mvpwlosw5x e)40N/m How much must this spring be stretched to store 2v/)lowe;p 2xme)wt s55 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What n8f(qd5 d3:r8gvo)mvco xrz(gjiw() is the change in potedq8z8 vir oo:x(m gcw 3()v)5rdf jn(gntial energy?    J

  By how much does the gravitational potential energb+vqh yv ql3sv7be 1-sj) e(7ty of a 64-kg pole vaulter changvyb17vesq qs j)-hb7 3+lvte(e if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontzg 0c/,vfhl z z b+bdxgjj/v/j/z/; 5tal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to resjcfjhz xz/d/0 blvgt+/b/5zvj/ ;g,zt 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 book from thedb r7+;qbcjm67sb2 t kt o8j1i ground so it is 2.20 m above the ground. What is the potential energy of the bt7b6 icd 2;jjbbr+stq81om k7ook 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 tws9: 6bsezfcw3 q6-w)s / dlebo the top of a 3300-m peak. 3:-s qb/s)9fl we6c bwszw6de
(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 tnl i/p6hd ,lb,ee 05j2f:sjbo 1c4jxjo a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end ijj p 6,4ocd0es hf/5n lx1jb,j :e2lbof the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabsu8/ crz,qgey- yo9zow3cj46s a vine hanging vertically from a tall tree in the jungle. How high can she swing upwaroc/g q -c syy8 u93orz4,zejw6d?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, sn2a6 zw 59wd(qx3xa kelides 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 shmxv8+n/pbl qob, .-l;l3 sjv nove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational potent 4rj16zq3 yhexial energy without the aid of a pole. Wiexzh16 q4j3r yth 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 verticallywa0gpb4* rw0y upward from the top of a platform with a sp0y0 b*gwp4a rweed 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 constn 1eim 0tswkkd5.dr- (ant is 950N/m is attached to a table and is compressed down 0.11winr-e5tk0 dd s.km(50 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 looped track sh0r*. ksdua 7r -ag(7vcrxc0 hhown 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 heigdrag.7chvuc x-hs 0 kra*7r(0ht h must it be released?    r

A block of mass m is attached to the end of a spring (s+kx k7f(eb+3wu /pj rgpring stiffness constant k), Fig. 6–40. The blopf/7+kjuwbrx+(kge3 ck is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whnviq ye1san-h6-6 o,1ifo ;th ose unstretched lengi1 ht,1-;n asqn-o6 ofv6iehyth 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 is dragged up tfpz11u , yb9n: ;0ics,l0oriw n;uylu o point 1 where it is released from rest. Assuming l swniz;u;yy ri 0,ouucn , p1bf1l09: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 ans.gxfa ct-9( v 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 pq ,57,wwh lbxklaced 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 spq7kbxwh l, 5w,ring 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 to2m (.zxr.,ild n5; 1zslrnvju 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 oppvd u+.;wja65ghll df 3cbu ;z5osite directions, collide head-on and come to rest. How much ther.;j5hl6fgwzd5u;3acdvb u l +mal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the1e yt* d)esv1 pfc ,po-z).oiu bottom with a speed of 2.2m/s How much thermal energy due tov .)p)ieo dsfo*1-uc1,ye z tp friction was generated in this process?    J

  A ski starts from rest and slides down :, cfi bi m. 4sjwxf0.c3zcwl6a 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 fef06muq; rwqt n2uru: midb/);p7;tnrom 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 mq4gtd 4 6g22mprf0mcs1w +fhq/jb u-o, and it bounces back to a height of 1.5 m. o0b1c+ df m 2j42msgwgh ftp-q4rq/u6
(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 h8vv8yp 9 jmr2a2e-xt pulled across 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 frictio9mrvpaj2 e8v8-h2x ytn is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of Imhzm4l vzj;+ 0f the average force of friction is equal to one-fifth of vz0m lzm4;+ hjits 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 foob4ett g*dd21w t of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attachob /m:0toex2 ced to a very light horizontal spring (k=180N/m) as shown in oec/ m:2bxo t0Fig. 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 the table?   

  A 280-g wood block is firmlyiwdu xmh rnl165 q6h2 rxy/9l+ attached to a very light horizontal 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 beyond its equilibrium position will it stretch on its first dx2umq xry 6/i9hlrhw6+n1 5lswing?    m

  Early test flights for the space shuttle used a “glider” (mas3(b/,y dr oz4mfda(lls of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air res(al f3m/y4(o bddlz r,istance?$\approx$    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 motuo8p)z tnn3 5xv aiwmf3dj0;d: n8 /rror to lift a 315-kg piano to a sixth-story window 16.0 m above? f8 rv533:r;jnnzuwddan/ p xm)0ti 8o   s

  If a car generates 18 hp when traveling at a steady )r- tz2omb c;ni2q wt/88km/h what must be the average force exerted on the ca2t;)-zim rno2q bct/ wr due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h inj zf56occy6y za42 eo1 7.4 s. What is the average power delivered byc oeyajoz 5cf1626 y4z the engine?$\approx$    hp

  (a) Show that one British horsepowe.us8v 4yntq1 gr$ \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 ivet20l c 48pa,glouu+:yg2j jn the 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 1150-kg car slows down froja)s*zej3zv kou*z12 m to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (wattsj*zv2au*k3 jse1z) zo and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor dop(,e-kr y teis /t/lk/ in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shotge uja:er,ejs /,s0wa.qu 27czr-a8 a from rest to 14m/s If this motion takes 1.5 s, what average power was deve7s ,. ajegu/jes rcwr02a z,- u8:qaaeloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. Whao.a2s/bi6u7u:ci a nhw (cwe4t output rating (watts) should the pump mot: iu7h aw/weoa(u.s 246 cncbior have?    W

  During a workout, the football players at State U. ran up9ud a 4g 4x2w1bayq9e wpg )th9b5qg(b the stadium stairs in 66 s. The stairs are 140 m l( pw4qhdeg49tbg g2b9u5 b awaq9yx1)ong 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 climbm ;+zp.j xfy3o.z mi*wvf.:kc -cba2y a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hl /b)b9s57a 7tquxeh y hzqk:,ill can it climb at a constant speed of 75km/h if the frictional forces ada b/7ku7b ,hxs)qhe :y59t qlzd up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be a-4*uhlg ok-hx80plwi ble to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 4h-lix- wh k0uo8*lgp0.45?    hp

  A bicyclist coasts down i: l 2gjxpm4cbb l7:q:7t;whka 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 desib.+w4m dgomn, o5) dejgned to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms af+ d,n) 4g mwj.obodm5eter 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 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first sbc q,-pm5pz,xhelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1 qm5x,b-cpp z,.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 lr fjb m:w7y/:gong jump (Fig. 6–42) in the 1936 Olympics shows that his center/ j:gf 7bwyrm: of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m slid6 me e wiz;ezk;;:ioy7ing without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very topeez:o7 ;ikiy ;mw ;z6e 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 without hfyozedn9 6zqu+rxy v +q- lzr.:p/9l8is 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 lvprzdzy o9.x qeq y l-98nu+z/:f+6r78 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 horizont *801jnviqe pg0e : xinn1l/jyw4vesi p23o p1al cord of length L whose other end is fixed (Fig. 6–43e v4os1ewg1/yj qil:jn10 3x 0p8niiev2pp*n).
(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 mountainhrgu( 3tt6s:0 zc4wt-fexe7( ;xcgz w. The climb is made in 5.0 h starting at an cw 6ewtrfzhg:(cgu4 et3xsxz t -0(;7elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a huge sy,xz. (cr2y ozv8auv1 pring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its pes9jbb3j r8,;zfa jdx3 9 kd60obtw ,lifts can move 47,000 people per hour. If the average lift c8be;z9, jkdajwxd6r p0j3fsto 9b, b3arries 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 8.6 iwmao+r0 ld)bnsu)h)6 gmy1 m before strikinl).6) ra6m0u gwn+ o dys)bmihg the turbine blades. 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 circular vertical lonr/m-f9)ymz(r*n4 25alfr hkucl j :h op (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 answ my4mrlu:nhfrl k(fczh *)/5 ja- nr29er doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could c(jerh69s tccr .tu n 99sn:hp/onvert a candy bar directly into work, how high could an 82-kg man climb 9j s6(/ntrecnuhr: 99. ptsch a ladder 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 otvnd( 4e -oe2hf 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale,ukm+j u;:v0ve 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 m, what does the scale read at kve0vum;j:+u its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake x:x.f;f6st/ f79xkhgg 3y1eg,yebsn (Fig. 6–45). He releases gtye f nhgx1e bxg s3xs;k,: .9f67fy/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 distance of 5.0 m indn:a;vaz -y1np. 2a /v lqfq5h 9.0 s. What minimum power output was used to accomplish this.5:vvnq nz/hya2 a p1;qfld- a feat?    W

  Some electric-power companies use water to store energy. Water is pumped by78ocw8hu,c hg-ug d fyxmmbl5 -ps3 xy;ln5/3 reversible turbine pumps from a low to a high reservoir. To store t/ 5x3f-mpccyou lw m8g7 ny5l8s;gu,-dbh x h3he energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness conh)z+f:w30)oe)s sjk )kts0fcwey )r nstant k is cut in half. What is the spring stiffness constant for each of the two )rns)tzc +:f0yo0s fwek ) )3hskw e)jresulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough .;62s qfyt)k 7dfjojhd 1uxy-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 ; fzr*k3dmk:5lmweh; i1ta r93.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and; t;am1rekk:5 9mzh irwl*3f d neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the pawq7bjvbx*-d +;zm a2z tient walks on an inclined treadmill (Fig. 6–46). Estimate the power requa-bmz;bqz 7 +djxwv*2ired from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance ofokpsq+ +k 9d h*.fkg9tm)u7ob 500 m, what wdk7.9hmkbu *o+k9)s+pqt of gas 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 m at a rate of 95kg/s (ak* :ii* oieri.) If this water wheel is set up to provide electri*.e:* irii koicity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s