In what ways is the word “work” as used in everyday language the same 8,2nd ilo)y3kevp jn4 as that defi)n28,kp ly4n jved3 ioned in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work onkg34bn;;fq; m c0bsc m an object? Explain.

Can the normal force on an oa ;-(jzy0q-jb/)sgwi ouacy0bject ever do work? Explain.

A woman swimming upstream is not moving with respect to the shoio :a2jh6il a:re. Is she doing anaia:jl:2o 6hi y work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider wh jaj06t9aef2 as ph*n9 srep(h7 5i9exat happens to the dishes when you pull a tablecloth out from under thpasip29j t6e5hxe a79r0a *( 9esjf nhem.]

Why is it tiring to push hard against a solid wall even though you/c ma+l67,znqxh e+.h 2rq qpm are doing no wo. ,xmp6q +qm +hchlr7enqaz2/rk?

You have two springs thatdu.8f pgtcd q-(+whh; are identical except that spring l is stiffer than spring 2fugt8 (+h ph-;wd.qcd $(k_1>k_2).$ 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 force1t lz9pixyyr h*2c( hsdd6*a5 on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a dis6t2*y1ca5 iyspl d9h( *rhd zxtance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational a5uj+4yedc.gv) f3ncpotential energy change when you jump as high as ce+vgfcu d. 54jya3n)you can?

In Fig. 6–31, water balloons are tossed from them3grhu u j7qrv:ru ov0j:) nt5;gca,y:o nb 32 roof of a building, all with the same speed but with differqyj3t0nu7bu):gav c5: r: g;oorm, rj 32hvnuent launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest pbz-w5 (cjr hh;cye// voint in two different ways (Fig vy5b-hc;w/ ez jr/c(h. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upa pl45odyof 5s.f;z,r right on a table. If you compress the spring by pressing down with your hand and then o; r5sz.y,dolf p5a4 frelease 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 s)d6d qxsl5 ff 4kj:o1zteel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without push1qjsk ):o4lxdfz5 df6ing it. Why?

What happens to the gravitational potential energy when water at the top qdz*z/nv.tw,8e a6sqcfi9j/ of a waterfall fall8 /dc zf ezn6q s/.*iaqt,vw9js to the pool below?

Describe the energy transformations when a child hom/ua-z iz 4g9t(v imn8ps around on a pogo stick.

Describe the energy transformatiojm: ;v. do1gn;2kc ahdns that take place when a skier starts skiing down a hill, b:m1ndd ; .2gjoca;vk hut after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the topk9gd 6oa 1 e. il1w5xcqbr :tzt7-(znm of a hill of height h and slides down. Does the vel (51tqd1-lirtk b.zc zxmgo nw 7e6a9:ocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to + t.jqx1s jk0qstep over a fallen log in their path rather than stepping on top and jumping qk j0js. t+qx1down on the other side. Explain.

Two identical arrows, one 9ir nk-a::/jo-yny xhwith twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster9o jnh:-xin -krayy /: arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple slc+9 u/j8ge rrwinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be g8 +jrle/cru9 wound up.

When a “superball” is dropped, can it rebound to a ne 7z 1*ei9xszwokt/ 68 hjp3aheight greater than its original height? Explainsi6o at3k z9 *ew ex/187njphz.

Suppose you lift a suitcase from thqx1m +.og1w2chlc0nc k u0g e2e floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) tcw hc+2qgng.0e 2ko1xlcm 01uhe time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power neewc els:utt1f c4+ ,*ibded rather than the work.

Why is it easier to climb a mountain 6-m58dpffwnc via a zigzag trail than to climb straight u fcpd8wfn56-m p?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropesvi+a9.s :yq ) jnt27 mqd*/wsje5roaz to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy conce qwv5 o :s+ 9j sq.i2ny7r/tjzameda*)pts.

  How much work is done by the gravitational force w68*syahzosql +7 1q2lk qup)8r 8lqe bhen a 265-kg pile driver falls+qz88 7qq lus2 l6)o1yh aqsb pel8r*k 2.80 m?    J

  A 65.0-kg firefighter clio 5eromkr92 4vmbs a flight of stairs 20.0 m high. How much work is requiromvr42 eo9k5red?    J

  A 1300-N crate rests on the floor. How much work i.lq5dhxw.nwts1cok 9 z8w. j *s required to move it at consta.*w9klcd1w.sotqn w8 xjz h .5nt speed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a1qibv n( 1dvb, 160-kg crate 10.3 m across a rough floor without acceleration, if th 1v1(bbn, qivde effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a forcke soev8vbxg x/0 1ax( :e11s,k-l mxhe across a floor at a rate of for 7.0 s. Find the net work gk1ssh1b/av vxk:,(8 mx x-xlee1eo0done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a tablet5li(q ;: s;tf:wf l6s;hb4ezjdpz 5r . How much work t4d5rp bjz hf(;wq sei;s ;6z:lf:5tlis required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff obje xpfio,rll(;8n (m-ry cts we might not otherwise b8fyl lro; p(im,x( n-re able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from acu nn0*mfl3a+f celerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.3lum +*nf 0nfa40. 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 ofxqz3ok1ws)0r mass M an acceleration of 0.10rzx3 k)o1wq0s 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 linear and 0fyt w/gfl(b+/q qn w3vb3-w athat $d_{\mathrm{A}}=10.0$ 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 :e 3zh5vukx ) i4 y5qx(rv7byialong the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = )3:b x (5yuih4qvzry5ie7 kvx 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 pr e)bfwk, /jv,article 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 molecule, with massl /52 *1sqs c1vixnnc8wyvd j3 of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its +6qxszy)q jjx+z+n b,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 elevk*.;tk p,faqram w bz.enwp /5)-+jbctron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 dvtvi-ko:9i./fv qdx14 x:0wajrtrr3 tv i)0f one to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from tsznpe:)k1/ v: o1 djya bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it ldj z: pe1 y:)tn1vsk/oeaves the bow?    m/s

  A baseball (m=140kg) trhv vojge7c ) zzbo6y:k777s3maveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the aver77my7 c 6be7:)vz zhs3vojogkage force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will itsz)/7/qa -. flwdm7 vv9ohthck minimum braking distance be increased, assuming all else is thhf9lcz7d- a/wv k/ o.)7v mqthe same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a(our/lt-hhdh 3 svs6 9 car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the o- rd3lhh6(tvu /h9sscar’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched* pc-yz6 (b(5ylw slp toaam)4 at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force oal osm z6lcywpp5t-b4)(y*a( f air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock g+1s d1dwxwjqi8n 4uf0o if thrown straight up by someone who does 80.0 J of work on it? Neglect air resistan+id0qu1w8f1j4xws nd ce.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by d)toiveha;.3 a single cable. Determine e;3at)ovi.hd
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much mq1afz;4 kis n*ust this spring be stretched to 4finz k ;sa*1qstore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch tvbe8z r-r /7.v n- yetyhonlvnr,/w)u4gj9n, o another 1.2 m higher. What is the change in hz tn- e ybnwv.rry8-4,u) ,gl7non9vjve//r potential energy?    J

  By how much does the gravitational potenti1fs99e(k ih 04iylaiwal energy of a 64-kg pole vaulter change if his center of mass rises a i1aw0e(9s9l kyif4i hbout 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface ha-nq4* wnku7s qs speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stifsu n-nq*w 47qkfness constant of the spring?    N/m

  A 1.60-m tall person)dwvact,z+ww + ad nhq1o5n(wl1 6:qj lifts a 2.10-kg book from the ground so it is 2.20 m above the ground. whntdw aqn1 5 do,6q)1wzcl++vwj(:a What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 )n +3l1yixau0 dbo*pa j.a.lvm and climbs to the top of a 3300-m peak. ). a. l*+dxyubai1n3 avljop0
(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 t e3cj 7 j6a( y(vjip9b,puboiizym(v338n d.to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is j6(p(9,i jnbyiz p3 jo3em7d yb8vcitu. v3(anow attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzvh:x41 c+o.mjmd ep-ean, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jung-d e h1mo.mp:+xc4j vele. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, startin.sxdr/::t ilb g from rest, 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 shoqn3213lhryqu ve 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 kinew71maui e3- f+nqxb7 b,n;xo jtic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed ouqanbxf1 ienm7 3wo7j;xb -+, f 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertical kl o71em3tbk;ly upward from the top of a platform with a speed of 5.1ko7be;klm 3t 0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constant is 9502xw f--0sm.lv)lslm8c c o.dlN/m is attached to a table and is compressed down 0.150 m. (a) What upward speed ca fl8. d0xl2lm-m).-c v slcswon 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 sl-7 j/swg:td qnides without friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at thjg:n qd/t-sw 7e 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 the end of a spring (spring stiffness con(vhsa l tq)r nm:7b+j;stant k), Fig. 6–40. The blormtv b+ajh: n7; (s)qlck 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 c4 f)h7osgkpr4 ord whose unstretched length is 12 m, and falls a total of 31 m. (a) Ca 7pgo4ks 4)hrflculate 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 show yoi 40mrerf.kc h0:y:n in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed at pointmyry.0efchoi: rk: 40s
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 of 3n *wcthny2n2 ;3 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom o,xz/ps oe5t y1 j7+sirj-pgac:9q g* qdy z)6ef an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, 1zg*i7xc,-ty65+ds egyqa /ope :r9qp) jj zscalculate 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 cycle up apmap1-ihsx )jrp 4ld ptb82o 4ak,m4c o4rg), 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, errs,q 6xl.t 11v 3 0qnzt3yueiach of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and3q.r6vqu 0 i zslyt,1 ntx3er1 come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends tgv/)0t 78;j4ht jx. ddvyo kza slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How mu7zttv jx0v)kh 8.dgtyd4/ oj; ch thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slid-q / .-n; ud-nyj/z1dfve:u (tlnvbzbes 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 froz7mnv ubq+1c,/tibxfe; w ,k0m 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 tpras-.pf4wa. zo, s /height of 2.0 m, and it bounces back to a height of 1.5 m. s 4/ .oa tz-rwp.pas,f
(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 fromr .xp7gac,yhf0j ye:ex16 d- v rest, is 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 coefficientvayxcdyj:. rp,he 6 70ex1g-f of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes poj go8 h,1da*gzint 1 with a speed of If the average force of friction is equal to one-fifth of g1jazd8h go,*its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s7w0v xu:r8 9iyf3domdcd+qq; reaches 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 y0au lhs;vfz. f 71(gespring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring syz( 7.fsu a1gle v;fy0hstem, 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 firmly atta3 )ey4k apbaa;ched to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coeffici;3a ep4y a)bakent 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 swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg inclppg e:vxc6yk/kk -76r uding 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 i-7k p6y:gc perv/6xk kts 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-samf2utpvz-4 0ny ;no5 5/,s7w.lb issgx.hf kg piano to a sixth-story window 16.0 m abogb4s h ap 5fyfti-7 xs ss/0uzon.ln;.25wvm,ve?    s

  If a car generates 18 hp when*; pgz5kbuw0k traveling at a steady 88km/h what must be the average force exerted on the car du zku0p;* w5gbke to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 zx 1( leka8y3s 65 x;x0t0fmbu htzkl, dl7v*es. What is the average power delivered by tmt3 86 *h( lfz vzab,;exl 0u7s5tk dkxexy0l1he engine?$\approx$    hp

  (a) Show that one British hn ))r/h3 vxtcyorsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “ki.ot-ne7 ma0mt 2hi io+lowatt-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 1 250f1b nqj1q/jptkgk150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approxi2p k gq1t n1bfqj0k/j5mately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 33x2 6oggr4 uit+2.h idlw 4nii h4ylk..0-hp motor 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 thiaf/ o5(k2dnx+buo c) ls motion takes 1.5 s, what average power was developed?o)bo 2x fcaknu/d5+(l $\approx$    W

  A pump is to lift 18.08 7pnrl js+j,og8:)kcoue ugz q/ g1.e kg of water per minute through a height of 3.60 m. What output ra8j+loqsj/ :u.)g ogkr8ge zne1c,7u pting (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium 4blw9gniw9czc(q l) ka7wk5)stairs in 66 s. The stairs are 140 m long ac(kl) qn49w7 )bwwiz5 al g9kcnd 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 it qmkukg/--4yj1b0;e /s g lxxs6-ug 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 1qymf2 ( gd661qthmlo8l eyl- of 120 hp. How steep a hill can it climb at a constant speed of 75l mod1ty m21 lyh6l -fq(eg6q8km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have ton 1fer, )gy7ojkmra+9 be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient ofr1fnaorg) 9j+,y7kem friction is 0.45?    hp

  A bicyclist coasts down a 7wk+xh8e2u gaa r t+o0sk m --o0rn2ab7.xf/ hc.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/,4mzu2b f8lll 6g3cmvj( .vct h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and isvublj ,(lc23tv4mcl6. m f8zg 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 off1mj z:vy*j v2vud 5.ed 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 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all tz yvvu 2*mj1ed 5:.jdvhe 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 s v su73vhb 0n7(c6eh px1pwu9ehows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum sp3 7uu7pbx1 eepnc0vv9whh (6seed 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 loope2xgnb; j+d,lz:k 5fhwd track shown in Fig. 6–39 is to remain on the track at all times, even at the ve j gd5bx2:l,fh;znw+kry top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370pn) )hy2j ,eld: j,3.30ao yonthcb la m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuy3,h)0j2ojypabh, :a.tnollc3 ed ) nming 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 horizontal cord of length L whom-z,hsxk4 r 5g qv,v0*qfy+lj se other end is fixed (Fig. 6–4vky-f, , m0vqjl5s4zh xqr*g +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 climbshyj y pn1wazv.0,fiyvm:7d-1 to the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calculatey 1:i1dm v,anhjpf.- v yz7yw0
(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 elevcvt.if nds2bcm+o2:j yl:m. )ator 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 can move 47,000 peopl7 wa+3-jlw g/g: 9gfqqmr qi1ze per hour. If the average lift carries people about 200 m (vertically) higher, estimat m3grlj 7/ gqw1qfai9:+-gwzqe the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at thwxkj a(+hgv(.1. hrmet7w u)ve rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculate+ahm .rhjk ((v)utw.7 1gxevw
(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 z7zd*g pui 0qcv, h.8ycircular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go throd8u.zzhq * p07yi, gcvugh it.    mg

  (a) If the human body could convert a candy bar directly into work, how c:r mv1w98o gh5i,emnhigh could an 82-kg man climb a lnrwo1e,9h:mg v8m ic5adder 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 upwar :;fw onyj1g7id angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom5uoce 7z11u5fha wi0aw+n6d f 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 m, what does the sc +ecadnofiu0a w5h6 57fzu w11ale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out rk96drd o(-0 3;wgtu uc/ fhiuover a lake (Fig. 6–45). He releases the rope when his vel/u-3idu 9(rcr fd 0uhkwg;ot6 ocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vvjg8;g:o/rx vertical distance of 5.0 m in 9.0 s. What minimu8grg/ox vj;:vm power output was used to accomplish this feat?    W

  Some electric-power companies uk ;*5b4skb 21a1z)ig jtpblxp se water to store energy. Water is pumped by reversible turbine pumps from a low to a1ztbbks*k 1;g2i ap4j bx5l)p high reservoir. To store the 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 constant k is cubma-djoc)8v. hc l)efv p 38z;t in half. What is the spring stiffness constant for each of the two resulting 8);8c3oel f.vbhd jv ma p-)czsprings?   k

  A 6.0-kg block is pushed 8.0 m +z1h fz;fe.pp3zo0iq 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 accelerate from 35km/h to 7/, akn-iorrbp.ezg/ ar4*d o 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 frrbkg iapzr.4/-o n/a o red*,7ictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient wal w- )aj fc/d+ovj*13,(o4wi q fiwn-ujxoig5rks on an inclined tr iw5fnr/j (ju1ojwg4 3 qcvf-oi,o*+ a)-diw xeadmill (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 dimo, rqf95p0rzc z ac;5stance of 500 m, what was its velocity when it5o;,0z5 r m9carpcfq z 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 (a) Idf-(ttph h/, yxt5q k0f thi ,tqyxkph d(t f0-t/5hs water wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s