In what ways is the word “work” as used in everyday language the samerr zhnt58pajmr 13k;,gr o* u2 as that defined in physics? In what ways is it 8*,n2atz k r ;o31rpjgm5hrrudifferent? Give examples of both.

Can a centripetal force ever do w l/c. o wsxe jrz7::ej9duw10work on an object? Explain.

Can the normal forcedmzwt );8r7dd on an object ever do work? Explain.

A woman swimming upstream is not moving with respec8r cd)*v+nzu1i/ykvy t to the shore. Is she doing any work? Ify *d )8iknvu +cv/rzy1 she stops swimming and merely floats, is work done on her?

Is the work done by kinetic frictijy. l3(b ef-ag (iuhk)cjdk74 on forces always negative? [Hint: Consider what hacb7 deh(lfk3j-ujk agy. i4)( ppens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard /h9/,cpla3ljf9flbjqpz iz3 ok 6vt87yq - 2vagainst a solid wall even though you are doing no wop,3zfk bi/a6jvt h y93pqvlllc -7q98j/ozf2 rk?

You have two springs that are identih8kar3 f avylq .2e+soq,rk -3cal except that spring l is stiffer than sprin+r2eo, k8-y3lkrqv afs3 aq. hg 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 hor; p uc 5lt9wl,vmocm07izontal force on a block that is free to slide on a frictionless surface (Fi wm;50ollt9mv7 upc,cg.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 howsr0ud+)a uee)a .ez (. 72dpjapit0qj much does your gravitational potential energy change when you jump as hig0eari dpe (e .tuz)da+j)0 qsa7j2p .uh as you can?

In Fig. 6–31, water balloons arm,a 4 sod k midii/755aw0q:eje tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on /m de dsqow55mk0ja4ii,:a7iimpact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest o6: aupw*e)fcpoint 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 penp*eo :uacw)6f dulum 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 yo ( p, t j,em*c4ezymxh:82fwcou compress the spring by pressing down with you,: (h w*ycoem mpe,cxfz 842jtr hand and then release 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 wire (Fig. 6–33)uqkj-d /e r* et:1j8jh. 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 without pushing i8/hquj: rjeket* 1j- dt. Why?

What happens to the gravitational potential en-w 9p +n2)y,o ska) a9nguks ;oujh4xwergy when water at the top of a waterfall py)ksw+42k) ,9 ;whoa-o u9sn a njxgufalls to the pool below?

Describe the energy tranq1 )6.rxh r,ex,xsn bfsformations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skii(o hbs s(p 6u q tyn,o(n::9cn8knayx+ng down a h +q(cksyoy( nhnb,s: t unp6n(xo:8a 9ill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top ma-/(2;t2 0mxl p puhofv wd-zof 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 ther-lvp - mu(fot2/ whzmdpax 02;e is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather 2wl k+3 dl0ufwthan stepping on top and jumping dowlld 3kwwf+2u0 n on the other side. Explain.

Two identical arrows, one with twice the speed ofld3s6rlb7;v v tw w*6g 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 the slower arrow? Explaivr3s6*gt6 v; 7wbdwlln.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) i7xw7oarc ss81o5p rj/* pu 8bvgnoring friction, and (b) taking friction into accoun*r a8u1psojs x 75rvw/8co7 bpt. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it ,jv -ia8/wo qqrebound to a height greater than its original height? Explain ,voj8/-w aqiq.

Suppose you lift a suitca2az ;fa:if2;o q6hw ylse from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it s;26 yfqw loi;2h z:faatraight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 foqp9:co+1(ir +f 5g:pfb vpz x3 qbge8nr the power needed rather than the work.

Why is it easier to climb a wztqhp t1dkcye0f9 0w.y64v 5 mountain via a zigzag trail than to climb straight up?cz5h94p16k 0td ey w.fq w0tvy

Recall from Chapter pj 1x)ivljt3 84, Example 4–14, that you can use a pulley and ropes to decrease the force needed to raise a he1 )3xiptv8jjl avy 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 gravityiff 4b f ccb-1p/ 6*:gor78+fpwrn0 glim6 naational force when a 265-kg pile driver falls 2.8nni4 fmr1rbgba/gcwo6 f 0- lf+*p76i: ycp8 f0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much wbb dag3ffgjy5h3 .c(;ork is re; c5 (bj3d.ybfa3ghfgquired?    J

  A 1300-N crate rests on the floor. How much work is required to move it at cons iv+co 2ml8+2mri mfl9tant speed (a) 4.0 m along o+ 2mvic m8 if9lm2rl+the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (hori9n gu r0b2s m qz4v2vt:(zuih0zontally) pushing a 160-kg crate 10.3 m across a roug2h0z t90 4q:bizus vv( rmung2h 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 of for4+p leqhk2q*(g34uubg rd7ci 7.0 s. Find theu+ 3g72 4*eb prquklg4hdciq( net work done on the box.   J

  Eight books, each 4.3 :/(vcc e ogt.(t(q-yl rco m+3 vq,gmmcm thick with mass 1.7 kg, lie flat on a table. How much work is -o yt.cm:(( qc+l t(em,/omgcgr vv q3required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects wgq66k i l )pipis:lce25 /w1nls9m6z ue might not otherwise be able to liff. Show that the ratsipums:k/1zci gwl 62)e9 q6 npi6 5llio 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° se 6s;x5;1sm l5xitxu+)v 15xar ufel incline and is kept from accelerating by a man who is pusl5;xevs; xiuefumx5 1 rals 1+5 tsx6)hing 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 gc;gjns)*(eb as+3nc q ive a helicopter of mass M an acceleration of 0.10 g upwar+s;a q*3jseg (ncbnc )d.    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 and i1r1p.me ze f)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 yar-c5py f(kop, 5:dyFig. 6–37. Determine the work done by this foropd5f c,a5:py- kyy r(ce 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 w6ddcc/qx3h2 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 mos uxo.kj.f xq,vk xxy 7dw374;lecule, 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 d0/6fsukbb +c+g,o ujboubled, 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 to stop an electronwf7t cs:)a4 k3pe 8nfw $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar travefm (ohfch4,x 3 nh3pa8ling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose stric:pxc1uw:d9 /d3 pf vy).nmwong exerts an average force of 110 N on the arrow over a distancecm)wcd:/:wy d oxf9 3vp.pnu1 of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m*/ j3 ff8vv+ 3zjbyh0p-munqa/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the a8pja0yfjm v/nz-vhb*u3f3 +q verage force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by1qfi9t8 z:vkd what factor will its minimum braking distance be increased, assuming all else is the i1t qk9 d8f:vzsame? Ignore the driver’s reaction time.

  At an accident scene on a level road, investi:8rq*z(mon p bgators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why :mnpozb rq(* 8does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time izuhath x75uomn p2x8*0m 07i vt reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about p7va x78ut z h0m5xm*2hui0on15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who 2/fog8 wquf fy/m43 ncz;+epq:1uwwjdoes 80.0 J of work on it? Neglect ai/23jwuf8+zw cey / 1 ofm f:4gwqqun;pr resistance.    m

  A 285-kg load is lifted 22.0 m ozavgypr;r z09/g11 cm v 5 v2xa+l*muvertically with an acceleration by a single cable. Deto maac u; 2g0lz rvxm v15v1r+yz9/p*germine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How muchsh,eu;6wia s h8fe:7 h must this spring be stretched to store 25 us s hw67,e:;hahife8J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.:e z:bkxt66u:w viuu( 2 m higher. What is the change in potekuie:zv u:utx :( wb66ntial energy?    J

  By how much does the gravitational potential energy of a 64-kg qd 0 .*-y xutq6dbc:a/cbi 3dspole vaulter change if his center of mass rises ad 0biqs-c6.qc/x :u b3tadyd*bout 4.0 m during the jump?    J

  A 1200-kg car rollin;lkhbb6z + b5f bu,wl(g on a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is thehwlbk;uzl6 ,b+ bb 5f( spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it (wpfy7m2tcxq)aw+l4;csl z9k 7vk2 f is 2.20 m above the ground. What is the potential energy of the book rzys2wmxkkt;l l q7w7(cf )a c42+v9fp elative 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 ab8ly;pwkvv pq btr k1d6g z6;-7d8c*mn elevation of 1600 m and climbs to the top of a 3300-m peak.8dpw*v -p;6 vzy8c 6mkl7;tkr1bgbd q
(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 spring v(+edd4 jwv8 lmo/j0qis 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 th e/4vjjwmdqo v(8d0+le 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 vine h+2i af b yiz.)tyvu5d:ylk;,r anging vertically from a tall tree in the jungle. How high caa 2rtu5fd: l)k+.v,iiy ;yybzn she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest,lb *s8(huul0p l/-1n hzcd p2s 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 frictwe d*uy6jdsor )izvnc0b 3z0+a6 .rl 1ionless 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 j 1p3nhn oh1l0energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross t jh3o1n1phn0lhe bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artvplg;*rgifs e*rd/,p z5n2g *ist jumps vertically upward from the top of a platform with a*g*z2dv g5/p*;fgrlnesip, r speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass9m wn p rztnm(17uct,:), 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 rn1tt u:wmzcm 9,(np7a 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 shown in Fig.rmsszh1 , n.q 03k(vtx 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 mus13x0 vtq, s(zh.nkr mst it be released?    r

A block of mass m is attach j9m ax3ile(5 g zdckp2vebs7pk;) y:6ed to the end of a spring (spring stiffness constant k), Fig. 6–40. Th z 6 )gbak;piykjlpcxe5:739s(2dmvee block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bun5.pqyyi d1:z bgee cord whose unstretched length is 12 m, an:1p 5zqyy i.bdd 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 to poi;u*h5 d ;tcsdynt 1 where it is released from rest. Assuming no friction, calculate the spee*dc ydh;5;us td at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown ul 4,jod9 -lgrwith 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 the2e jiypi(r/21ta:uocwo wth f .4y6 d0 bottom of an elevator shaft. If the elevator cable should break when the elevator ish6edt (piw/: t rj4fyc2y 0.2i aoo1wu at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycb+)s i f.qz;zdu-(ah ile 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 ydh hf1 l,rdcsqo/1*1 traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal e1yhl qd*11fc dshor,/nergy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and rea erb2 u1yakfem u;4q1h e6d*/kches the bottom with a speed of 2.2m/s How much thermal energy due to friction was gena q2hu4;1yre e6 *fdkkum/ 1eberated in this process?    J

  A ski starts from rest anbx+-b7ak xvk *d 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 a tree 13.0 m above the g1dutek) bg(u (round.
(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 hbu,gvt-inp6 .x4mz 2xeight of 2.0 m, and it bounces back to a height of 1.5 m.p bxi.- mtn64 2g,zvux
(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 in t7 euqc4s+efx1--fv;t kk(a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for t et4nst ckvk(e1xf7i-+ ;qf-uhe next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coa1es8jx *8l ,uori4 kcoster in Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance trav ,4cex*8ool j1ik8usreled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reac3k--pi uv k2pwhes the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal springp ne+1wr e5xsh.pp+q9 (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 equilibriwpepns+q9x 5p1+r. eh um position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fi)pr7oxl e;m5u g. 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 p7ux e5m); lorfirst swing?    m

  Early test flights for the space shuttle used a “gliderq4m0.cihld0of m6+aibl z mom0j,3; n” (mass 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) Whatj,ao . d6mz;omm43mflq ni 0+lcbh0i0 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 ,s kxg .ag+fy-z7v ihzky3*j1315-kg piano to a sixth-story window 16.0 m abkxzkh jig *sy7v1 -+f,zyg.3 aove?    s

  If a car generates 18 hp whenf(lvh imb(8 0 n:.yr*v byyuz*w pca-1 traveling at a steady 88km/h what must be the average force exerted on the*( p1y w8*cv ly 0fhb(in:-ya rmzv.bu car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest tm /c5yhp6+xz -s caoe0o 95km/h in 7.4 s. What is the average power delivered by t +pe5z6c yx0mc/oa-hshe engine?$\approx$    hp

  (a) Show that one British hgfz) lpv()n 11qsqn j6pq)/ldorsepower$ \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 tsgjb t.+y*o e9i)d*dm he 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 df:a4 z2y rf-riown from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (wafrfza :2 r-y4itts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 5k6)p*nrf bhih? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this ggspc 8gd5h3k1gis-:ndj7a1- epo x *motion takes 1.5 s, what average power was deve:gk*gspoip d8jca1g- 3xdg7eh-s5 n1loped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.6 ksb,z2lsr3)6mk zb1ku;tlv*0 m. What output rating (watts) should the s )tkkb;m36zrlsk,v2 bl *u1zpump motor have?    W

  During a workout, the : h*2o+scqdahfootball players at State U. ran up the stadium stairs in 66 :2+dhahqc* oss. The 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 cycl: nm5uffdp( lz7i1vc .ist climb 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 hill 3l :2vq aenqy,can it climb at a constant s:2ne,qy 3qav lpeed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg b 2igb9aqnh i n .79wy7cc(-ugzox along a level floor at a speed of 1.2m/s if the coefficient ofig7n9.iq2-hzyn(c u cw a7g9b friction is 0.45?    hp

  A bicyclist coasts dow0st;zq *kc)tb/wx *oan 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 c2uxw/2 i j(z:bazbgj1 ijf .n9ars have built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effec1 zwjj :gjfi9ba2x. (uiz2 nb/tive 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 f(y r1v*gtc2qthe first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm abov2tfvyrq 1 c(*ge the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics sht /o; whhr/cmwgj yv).1 j b(e2yju78oows 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 wa/wjrh v;)w2 1(ujj/mob 8.tye c 7ohgys traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding wit rft9mji-dta5q(prto7(3i 6 p hout friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of thm3 fapiqtoj -r 59t(r p7t(i6de 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 w og defm;td .ii,(6fs4ithout 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 and his termina; f(it4fego.msd,6i dl velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose ozqg8oe 6bi +(ather end is fixed (Fig. 6–4+ eiab6g8(ozq 3).
(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 ihgb)3 nc((i*qy an5een 5.0 h startg5 in((q a cnee3y)*hbing at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920 (eh5v7e6capqwm g +7o-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts cyge2u4 w,dupf34f mx+an move 47,000 people per hou 4d4x+fuuwpgy e2m3 ,fr. If the average 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 iqq/tu.8ae6m 3eetw 7 1)hx wj650kg/s and falls vertically 81 m before striking the turbine blades. Calcula xee 3t/weahw jqtimu6q)8.17te
(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 xr6 8juqet*rs6*om :l a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop otuqer 8o6l ms*6x r:j*r how fast you go through it.    mg

  (a) If the human body could convert a candy a4:bds7:2kukq rjq . lbar directly into work, how high could an 82-kg man climb a ladder if he were fueled k lqu4d sq2a: k:bj.r7by 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 4mz0l k ddr43btvuj7;+g rd*w55.0$^{\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 bathrooms*dky 2sv) r+m 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 heigm)v+*kr syds 2ht of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fi69xstg6yh h* yx9fc,rg. 6–45). xgfxys6 9h*9c, rthy6He releases 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 cli )smbw:p88 oqwpel/e ,mbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accompli 8e)sm8wol /pqeb:pw, sh this feat?    W

  Some electric-power companies use waterpav*v,bz9; vpvek). d to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energpvdbzp)vv, .e vka 9;*y 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 k is cut in half. What is (4p v99 i8lhen. zwrqxthe spring stiffness constant forhqlzw(9ven8 r.x4ip 9 each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37 -p sjtx6j5u e,3zmk)dne vxw es,e.2. $^{\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/*wv/qxz 5ag zgr k;np;; 4 0(2lzsxqzzh to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional lossesrxzwvqlx;40zk;p szqz 2g5(z n;/ *ga.    s

  In a common test for cardiac function (the “stress test”), the patient walks on v9n:z f*q.bg;/u ucgsa*-l2egtg1vg5elq m( an inclined tread(ge;n e*a *bv9 5vsc2 /qfuuz:1m.-lgqgglgt mill (Fig. 6–46). Estimate the power required 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 of 5 n:jlyml.(lh7 00 m, what was its velocity when it left the volcano?jlmh y:nl l(7. $\approx$    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 l)e,4 jpof3 b0u6t fbrroyt5+a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what bb,y3 j4oltpof5 +r f6t)rue0is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s