In what ways is the word “work” as used in everyday la055gn nl v ikv2vr-fr5 b0-cvsnguage the same as that defined in physics? In what ways is it dif v-rvnv5sb2cvf0nk5g0 i r-l 5ferent? Give examples of both.

Can a centripetal force ever do work on an object? Explpfu7d s2zg v82r5ihpus,-9r(ua4l b tain.

Can the normal force on an objzb ctfm.;2j8gect ever do work? Explain.

A woman swimming upstream is not moving with respect to the sn+suhj - 5f;y7:56 w doi 3vy:qvlekuohore. Is she doing any work? If she stops swimiuewv : :56u7+qdl;oy vf3h ns5koj-yming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consi4rm 9 z;;ae0xw wu.rspder what happens to the dishes when you pull a tablecloth out from und. pa; wumserxwr40;z9er them.]

Why is it tiring to push hard against a solid wallz0 keeh zqwft. 5959/d2 vlsqp even though you are doing no w.edfz/zpqs 2l vt 059w5ek hq9ork?

You have two springs9xls/ l,) nh:u+wz.r s gooi8y that are identical except that spring l is stiffer than springozxy /w+i.l ,nl8:os rh9g)us 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 horizontal force on a block that hf3-d: eet4m subjd/, is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the b: de,- 3htfjm4/suedtime 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 much does your gravitaty w7( :giw6uv * bpez.y6fq,jeional potential energy change when you jump as high as you cab j (ywwf.6peg*6y ue,z i7:qvn?

In Fig. 6–31, water balloons are to5*xcg;fx hqc7 ssed from the roof of a building, all with the same speed but with different launch angles.x7cf;g qxc h5* Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from cxl ) g:7ea42qc)f5 :e jdk7js+vrpkb a point that is a height h above its lowest point in two different ways (Fig. 65j 7k vrsc)q j2akep):f:g7c+xb4 del–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 upright on a table. If you com: z2db+z-(cnnl.*xwlu;s *jl*th fb apress the spring by pressing down with yjl c bbxs.l*2:-f+*a n(znzdh*w ;u ltour 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 o /nfaiuox-l*b,ib 2c0p6 d ikpgd94+ (Fig. 6–33). The instructor pulls the bafc*xob0k-gpan6 b2/pi ,lo uiid4d + 9ll 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 it. Why?

What happens to the gravitational potential energ) /fd1pto,ahn y when water at the top of a waterfall falls to the1t,)n/ fad pho pool below?

Describe the energy transformations when a child s; /x*cu0 th,uxnyf4oh4+zau5fjkm * hops around on a pogo stick.

Describe the energy transformations that take place f zqmt;dg/ 7t(when a skier starts skiing down a hill,tdgq;/z7m(f t 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 of a hill51/einr jwu:u of height h and slides down. Does the velocity at the bon5:je/uw1uir ttom 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 strzl-/yg ld,9h ut sg63ep over a fallen log in their path rather than stepping on top and jumping down onggzru hd,3tly sl-9/6 the other side. Explain.

Two identical arrows, o; w.5(ocnm49detvy;nt p h 3myne with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional fo (nne;tp45.m3; d9 yhmwvytcorce on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (amra s ;v4v1+lsmx:y1u ) ignoring friction, and (b) taking friction into account. Explain why a g 11uxlrvmyva + sm4s:;randfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its orino t,i98r*z+ qat c3haginah 3cz+q, t*9ro ianta8l height? Explain.

Suppose you lift a suitcase from tio)(/fvodm: - khk5: 5urnhmp xo/e2che 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) the time it takes, (c)uv) :/io:kek/ -( mf52xphmooc5nd hr the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 fo)n 6yvsu9 1xarfm72f*5hpugw gg5m;cr the power needed rather than the work.

Why is it easier to climb a mounttx7y a;5/g-md spar7oain via a zigzag trail than to climb straight up? 7-5 p;mg /7dyxtasaro

Recall from Chapter 4, Example 4–14, that you can us+rxo/7v ecn,s5/am(cy * xdvoe a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). Bu(sd/r+ ncvc xm/x,av * oe75yot for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when ao kuua*ezwaw2rgxnff858 u/f+ :i7, p 265-kg pile driver falls 2.802u,w5npe o8 xwa :gf8f/irku +azu *f7 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m hi k.4o11uyt ejqgh. How much work is requ.q e14yo1t ujkired?    J

  A 1300-N crate rests on the floor. How much work is required to move 1c8bm u9aj9 nhit at constant speed ba n9hcju9m1 8(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 5e.bnig/0m xvdo (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction wa0b /emi5g vnx.s 0.50?    J

  A box of mass 5.0 kg is accelerated by a force a0s8-kya17n ws6kd 4z mwl bp:pcross a floor at a rate of for 7.0 s. Find the net work done on twlps-knd k 8:ayw7mz0spb614 he box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How mux w8 yta;wdv+e- g)z4ich work is requiredz)xv+w wtdy-4;8 ie ga 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 we mighi.l8y* d(rc*0fhrvwyt not otherwise be able to liff. Show that the ratio of output forcer *0.y(f*hrdy 8iwcvl, $F_{\mathrm{O}}$, 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 ai.dkgz 9ls+z ,xu,+rq6u q-b kccelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The u,9k i qbrz.+g-s,kdx6l+zq u 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 reo6 t. e//sc:ujvcbls5quired to give a helicopter of mass M an acceleration of 0.1je6cv5lsscbu /o /.:t0 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 t)c2vm wznwm : (4y5s)tyfy/ef 7nqpb*he distance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the xahdmgm w)ojeulm75;w t,j) x: g)y8, /lkdg8p axis, varies as shown in Fig. 6–37. Determine the work done by this force to move thel :ho,)egl)7y/wu),jxm 8w;kg8dp5dm mga jt 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 au5m+ zflo(8 lon 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 og/p dn1mg 2my5xygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by whbesq e98k,k;+ cupe 09 ydtwn6at 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 electron w h/dr8x fg (l5lh0o+g$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 traveling at 7dy00al6) 14g vwro u1c) snaxo 8fowg105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an averagqd54m,cadc 8ke force of 110 N on the arrow over a distance of 78 cm. What is the speed of tqm4 a k58c,dcdhe arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s mg ngbqq/ tdp;),66ubp oves a fielder’s glove backward 25 cm when the ball is caught. What was the ag tdbgu )q;/bp,6qp6n verage force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum j*gd+e sdjtj v4md,(odv83,i em7 ( dibraking vg*3mjd8(4i d +(o ,7d eseidvtdjj,m distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene z2 v )bcgl/rq;5attd )9nfl/td 4 xp1qon a level road, investigators measure a car’s skid mark to be 88 m long. The accident ocdc9bd l nqr)/t /l ;g14ax)tzftpv52qcurred 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 car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time rhh39 0bw+hw) wp: hs8t,yh:y2yht q.ud ps1hit 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 i. 30w hqdhh +ps:h hs wytrbu:9p2hw8,t)yyh1s about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does 80.0ib ca,m96t(h l J of work on it? Neglect air cmli6ahb9, t(resistance.    m

  A 285-kg load is lifted 22.0 m veut h6ci2xvq v) cp/0844rajsprtically with an acceleration by a single cable. Determinacpcr4jv)ihup qxt802 46/ sve
(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.i7y+za y r f+a25djix, of 440N/m How much must this spring be stretched to store 25 J of potenti.+ jd+i5 f7a2riyzaxyal energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Wha;c,bws j3fis)*jc gy/t is the change in potential energw ;*f3c,j)c sgyjs/b iy?    J

  By how much does the gravita clw0fzh qigz sn+5sv7;92/titional potential energy of a 64-kg pole vaulter change if his center of mzl7zti;n + 9wv5q2 cf0 hsig/sass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on xutxo9x f)n-)a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to resfo xn xt)-)x9ut 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 the ground so;ow dg i0q:4r 1qi61r)lycfjm it is 2.20 m above theri fi)01 m1ljqrgody;cw q:64 ground. 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 m and climbs to the topf64 6vq vqmnj8e/ ffhs08svf) of a 3300-m vq/6)qmvef ss j084n8vf fhf6peak.
(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 nexmqztrlmh8 f;5ql80jv6uq1 5c ec6ha :t to a ruler. The end of the spring is next to the 15-cm5 rlh 81q6j zl hq5e6m;f aqmtc8:cv0u mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/xl wr0-:;jgmf s) and grabs a vine hanging vertically fromjwglrx0;mf -: a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionlespt:jm9xjf3p 55i- y nss 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 q q2)w3ma w:rja 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 energgad.amgkt5u 0mkj m( +a e-4l;y is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave thdle(5j-t u g.aa4+;gkmam0mke 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 verticallywv6x -cpv lczk51u;zi//vl gztl )5)q upward from the top of a platform with a speed of 5.0 m/vkzpt)g/cxq-zl 5v/61 ;cilu w )zv l5s. ($\alpha)$ 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 950N/m ix n ,gnbuy+f ha40t*i,s attached to a t +,fxi y4tun*,an0hgbable and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides withoutuvi0 v;b-u u ftc6v2l/ friction along the looped track shown in Fig. 6–39. I;bvvlut0u/i -cu f2v 6f the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the ejh m 64:lo 6o241mnkrwigp7ja*3c mz und of a spring (spring stiffness constant k), Fig. 6–40. The block w6kmoh4om6u n* z3c12jl7:agjpr4 mi 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. S*o514pwh daypx;,r dh +r2b k).y zvvxhe is tied to a bungee cord whose unstretched length is 12 m, and falls a total) x5pzwxh2arybv h +4 vyor*. ;p1,dkd 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 sg,w+ m(- ad4cc)wmxpshown in Fig. 6–41 is dragged up to point 1 where it is released from restmgw,xp(ca- w 4 sd)m+c. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed+odmvdhr9,8hi:c jv( of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the botto(ixvgf5/e0o vm of an elevator shaft. I0veigf5 o /vx(f the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that 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 cyct,6i.ifdl-d:ew5 duqle 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 opposite -m94ra/mcbv w directions, collide head-on and come to rest. How much thermam9bmw/4-r v acl 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 + hdf0,lfiko )u 2zz0sreaches the bottom with a speed of 2.2m/s How much thermal energy due to friction wao)+z,lf2 ifdu zhk 0s0s generated in this process?    J

  A ski starts from rest and slidesi u5tah+s)bz . 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 droppeop5 t qjx*/t; ti6wp;gw)p2nf d from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a hs uur r gkga.g6,zb.u2jy/8 fnv:-4eaeight of 1.5 m4u,: a rk sbej-n .rg6zy8v f/2uau.gg.
(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 pullc3 :0ai:wrm9hfb et6 ped across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionl : femb rpha0ci9w3t:6ess, and for the next 15 m the coefficient of friction 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 If thb +t3cf apg0uuo9 n12ie average force of friction is equal+ tu2319igou bf 0apcn to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s r5(fa8o5 pjv+9uun lmceaches 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 acw:6 pr70hc ta9vdu;bttached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stvcbt79w :0 ch6urap; dopping 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 ligh(w3ym7 oi+wjg--bo f wt 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 th-g(w +7f imy3-wjo owbe 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 spac 0d+xwfz gq52:x/fhsbe shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider fwf/ +qbd5:sg2x0zhx eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take .keb-csvfvt88u ,gu)zpvx-- a 1750-W motor to lift a 315-kg piano to a sixth-story window 16.0 ksvzvvbtx -f8 8 -)u egp.cu-,m above?    s

  If a car generates 18 hp when traveling 6+gqa9d7qo-/xqm innh- d m)t at a steady 88km/h what must be the average force exerted on the ca7mhai-mgnqdd6 q)- to /9q+x nr due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to.sk5wcb f xgn .u:77yj umf3:o 95km/h in 7.4 s. What is the averagef.o77k:3w bxsu n fcj u:y5g.m power delivered by the engine?$\approx$    hp

  (a) Show that one Brit yc4nh5 bv at0u(vto:8ish horsepower$ \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 thil7+kd2z7x sre 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 from to 0:) cq;zj k lukkiu-p:sk+l6 a65km/h in about 6.0 s on the le 6- kz l):;j:pckualqik +s0ukvel when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motoqe og vkmr2it4m,+ n71r do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates/0nmz5 1 yapu2fhcd .i a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power was imzh .fn1p/cuya5 0d2developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m.d+ai pvvx-f0h0 oefje6 z0.q 2 What output rating (wattjzvp a.feiq0hxdo 60f20 v+e-s) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadqd*qs dtqbc q*:tq9;er;v5j:tad g43 ium stairs in 66 s. The stairs are 140 m long and inclined attbqj;q t ed3q9:s gvq a*5;qdtc4r:* d 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 d*t pt /m mmdmb02:e8da 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 pz0:sc isxy)uchgn*pl4 6jb::p r g16maximum power output of 120 hp. How steep a hill can it climb at a)p 6gsg psr*nb:yl0p6:iczh4cu:xj1 constant speed 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-kgj5g . mk;x4zpj box along a level floor at a spejmgp4k.j5x z; ed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 72ea9r7n- 3 d pwqyyw9z.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” th8/cnh4-jgdjm9t-i g aat 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, asi4 h -ggtc8mnda-j/ j9suming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the rr orm.sgxs)iz *+(bfi hv 3a8+p*b.hremaining four shelves are each spaced 30.0 cm above the previous one. If i +zrpa s *3h8 +hmr)r*.bi.vf sbo(gxthe 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 Olympicsh h34fq;( ver30km tgf shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum q 3 3(evh4mhgfr;ft0kspeed 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 looped track show tsso8w;4z+x+kx, tnkn in Fig. 6–39 is to remain on the tra tz onx4xk+,wks+s;8tck at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jump.yenet 02; 5jjqab5 qiing from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’nqjj q b.0y; ieae55t2s 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 whose ot sq(stshay 208her end is fixed (Fig. 6–43). qha2s8(s y0st
(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 a;5yzays )ng g ga))n*made in 5.0 h starting at an elevation o sg;an 5))gz*ayagyn) f 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-k,fiq jjdu r;-cb 9qpi36u+ *odg 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 can move 4nt4xm/9; p udn7,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power neut; xp9md4n/neded.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically )kayzla*: r++ f0itss 81 m before striking the turbine blades. Calculatea+*: azfki s+y)r0tsl
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), ruy+8q5efsj o-l(5j tthe difference in your apparent weight at the t8-fyr e jq5ljs5( ou+top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar d ,d ne4glos.129 ; x-3kkmkh(xsnnli xirectly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=g,nd4 (kxn hmxioes2l-.n3 k s1; x9kl1000kJ)    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 45cmt mcwj5l20 5.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale comprey.3 d,c8cdywp sses 0.60 mm, and it tells you yyp8 3c yc.wdd,our weight is 710 N. Now if you jump on the scale from a height 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 ovlew5 7z79ldnwe- 5lavb+ (i w*(geo mmer a lake (Fig. 6–45). He releases the rope when his veemwla l *w9zd ( 5m7l5i7+-vgewen(o blocity 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 dist1uzyxs ld1 .(p+dho ta(1s j/kance of 5.0 m in 9.0 s.k1ul y+/t.(ad h1d( sspjozx1 What minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Way 2v7 4 k0p,tkxtjb2upter is pumped by reversible turbine pumps from a low to a higv 7ytx4 b2jup2,ktkp0h 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 stif 0z0fq5+:;soj mgkcy jfness constant k is cut in half. What is the spring stiffness constant for eac;moq jky 5g:c0fs+jz 0h of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a roughy-+kqcm 3yoz 01mnbky z8s+m5 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long willm1t bxf4(ambo/z -pjx9ob1 w. it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and 194.f mx(jmo tbbpa/-xzwo 1 bneglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walwzlf)q.0*x + ie7b olcks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the lbo)+fiqwcl *zex 0.7treadmill 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 500xv 8fm)o+ 2f0davjx s2 m, what was its velocity when it left the vovxaxv+208mj ds) 2f folcano? $\approx$    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 fry8 . ,f bpxvbj8mc06esapk7f- om a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricijk psm6fx, 8f.e v -bc7b08apyty output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s