In what ways is the word “work” as used in everyday language the same a *t(-.fm q lh+okky;jv+3doi js that defined ik-t;o(d+qi * mk h +v.jlfyjo3n physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an obje4 i,a6l /barqbct? Explain.

Can the normal force on mtcipep.q xk27j*9ubnre/ 4w up5z4 7an object ever do work? Explain.

A woman swimming upstream is not moving with respect to the s.exnqsf9dvqy- , n/n; mo6z-t hore. Is she doing any work? If she stops swimming and merely floats, is workx ,n ./n t ;d-zmf6-eq9yqvons done on her?

Is the work done by kinetic friction forces alwayb *uzt7 ulk,)ms negative? [Hint: Consider what happens to the dishes when youz)ubk ml *t7,u pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid waokp2:m fid +8fv ).ucjll even though you are doing no wo 2ov :mikjc up8ff.d+)rk?

You have two springs that are identical except that spring l is stiffer than spr1fie,. 2ee bpqj;c dr+ing 2 2f ep1 r+ede,cji;.qb$(k_1>k_2).$ 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 ikrx yoz v0r5n :86wbt*s free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and brt:v 08bnw *5o r6ykxzy the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your growudhj(uu*;n t97z8.ewa o*favitational potential energy change when you jump as hn jzw*9d. uw*ua8 o(7thf e;ouigh as you can?

In Fig. 6–31, water balloons are tossed from the roof of a buildine tbr)jc6+kefh4 3u )sdc,cm86exap) g, all with the same speed but with different launch angles. Which one has the ht s6 dk) )3pc,ce+f4 cbejx8mre6) ahuighest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest point cic6.;9g e+;tms nq6 lmvs3wz 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 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 anglem3csmg nsvtql+i.cz6e;;9 w6 from the equilibrium position? Explain.

A coil spring of mass m rests upright on a ta ;3ucrd9bae-p ble. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservatioer 9bcd3;ua -pn of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33) (u8lv tl8:heq-;ba1mvyy1lr . The instructor pulls the ball back and stands against the wall with the ball againhqm :l1 lavv e-(r8;lytuyb81 st his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential ener6v2ht lx w75zxgy when water at the top of a waterfall falls to the pool below? hvw75 l2xzxt6

Describe the energy transformatio bsom.,ej /yqk47zgwh ::t.lsns when a child hops around on a pogo stick.

Describe the energy transform .bpq+w7x lvm;ations that take place when a skier starts skiing down a hill, ;q7+bpx vl.mwbut after a time is brought to rest by striking a snowdrift.

A child on a sled (tocw n r6bl(k(,ztal mass m) starts from rest at the top of a hill of height h and slides doc 6(l(nrw,z bkwn. Does the velocity 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 s1y pzn8yn8/ ah6xpq cw:(he+to step over a fallen log in their path rather than stepping on top andzyh:6s(pn8+p c h 1/ waeqy8xn jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, 5qys/y *ye( 7wi8unkaa kbv(3are fired into a bale of hab v*an(5iyu83e ky7qk/wsy a(y. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simp :1 sqyopia9mn 3ab8 vtn)g55ule swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfathery538n51 9 :bsqatmunv pga)oi clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its orptiag5: 9oy ( 1jna xr70m; ecx)n5kkliginal height? r5 x9k)on e mkt;c5 pi0l j:n(a7x1ygaExplain.

Suppose you lift a suitcasee 5-rbp30uz k xkej*e, from the floor to a table. The work you do on the suitcase depends on which of the following: (a) w3j,5xbpekek-r*0ue z hether you lift it straight 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 for the power needed rather t4* ;aebitsa,sus-t f;han the work.

Why is it easier to climbww b1oj-i/cmv/l 6f5 r a mountain via a zigzag trail than to climb straight ul/j fr5mb -c6ww/ 1iovp?

Recall from Chapter 4, Examp8znqfa12de -df ee ehk9606im le 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy lo6eihf ad86ez 9m2dnkq0e1ef- ad (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile m g)gcm 4 6l(pztvxl)u*sp;o,driver falls*m us)zm pp ;tclx)( o4gv6,lg 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of .*q3x;vae 3jvgr f q*istairs 20.0 m high. How much work is require*3ev*.qqgj v; ixf3rad?    J

  A 1300-N crate rests on9 ir7hb2wg5s ; eu8p2x v)f-3higaobm the floor. How much work is required to move it at constant s;x8 i vbrwb37o 52aehf -ph)2ms9 iggupeed (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 (hoe 0wj0(f;wlkefz:sc/5 zw wq+ r:jm*prizontally) pushing a 160-kg crate 10.3 m across a rough fl/(qwezfzrs;*0lkp:cw wj wejf0 +m: 5oor 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 ai7 fm:v .a;le5. w(h hum)6 guhk)tcci floor at a rate of for 7.0 s. Find the net work don;a :khei)mhugt7l(5cuf c w m6vi.h).e on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a trm ,vnxif .,p7able. How much work is reivf,r.7 n, xmpquired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff **cwwg5 4ctlb,nv(-8pvi1j b h,ctndd2ms *yobjects we might not otherwise be able tid(v* 1cpdbnjc*tvws -h 4,85m clt2 ywgbn,*o 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 2ld-33f;*jfme f/u ixr 8° incline and is kept from accelerating by a man who is pushing back on it parallel to th *m;fuefjd3 /-3i xflre incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicofkk :cuuih; l /f99gp4pter of mass M an acceleration of 0.10 g up 9l4 gi/cf;ukf:hk9upward.    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 andx(0hwpys, 11xzw4 q lp 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 a u:-yovshi h yfgy54k73 bsp07s shown in Fig. 6–37. Determine thk70yy4 7-gu5fbsiphoh y:3 sve work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts in the k;m,*stnuz f/ gj22wa $+x$ 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 mass of -j1 9-g-c fd- jmvwawg$5.31\times10^{-26}$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 vf6l x2en-qt r.-r2kjwhat 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 requ8 qexahp1* ip:e+e- wnired to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250)fl )u yhywub 2p45by y-7xd-j-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average bnr 7xk-s r*3ql0 fjy/force of 110 N on0/l-x b7jrs3frk* qyn the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backwartbde4uwy00oam8ar00g9emv/yh* n) x e / sl;bd 25 cm when the ball is caught. What was the avm9hmt)wee u4ao /rxl ya; vb0g*nb 0 008yde/serage force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by whdbvhomld6sz i s2eit d e;+/*vv+:e58at factor will its minimum braking distance be increased, assuming all else is thdds/6 itel2:v + vb *h85se dz;v+meioe same? Ignore the driver’s reaction time.

  At an accident scene on a lev po;rhrnydo -ri8meylw (5 2y*5gm ,x-el road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a,y5m2g rpo8-imy-on* xry(lwd5;hre 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 t o9gkx hajl ma)(dym;;p 0(8xiime it reaches the plate, it may have slowed by 10%. Neglecting gravit m;ai80 9)pdyxkhmj;( g(l oaxy, estimate the average force of 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 go 1 *kke( epzxv kbi;-eu +sfd2+if thrown straight up by someone who does 80.0 J of work on it? Negs2kzifuee+ *1;x( kep d+ -bvklect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratiozri4f (*8t.xzsivm *w at ,q1bn by a single cable. Determi xr*s1t*,wbtamv(.8fiz 4 z qine
(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 2:f hgf 4vsjsh(vyt )(constant, k, of 440N/m How much must this spring be stretched to stor: g )v2hfsyt(v hjs4f(e 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is thzbkg c bw jnpj5ze ewi; ug1:ej058g-6b0,x+ he change in potential energy? ik; b1:wz cjgp uzb8h+5n6b-, g0e50 jxwe jeg   J

  By how much does the gravitational potential energy of a 64-kg pole vaulter cuahelm/40eb.bs.qt +o h f,5rhange if his center of mass rises about 4b m4r/teol,+u f h0..sq5 hbae.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal bn(z1 i;a0 t:hu,nlrfsurface has speed v = 65 km/h when it strikes a horizoz;nr, (i tb :ln1u0ahfntal coiled spring and is brought to rest 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 it r /)8k+k5d:m nzz vqmyis 2.20 m above the ground.m+ 5 nqvrm8)z:zykkd/ 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/w(lvz27 . vhi3k8 w .zuxmzuw elevation of 1600 m and climbs to the top of a 3300-m peaku.vz7wmlk.x(8h 3/2 uzw zwvi .
(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 thenu.0z rcfm x q+ zjz(,a(5qkm4 spring is next to the 15-cm mark on the ruuqnq.m,(04ac j z5mz( fz kxr+ler. 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/s) and grabs a vine hanga)wu yq f/nre5hy:h :;ing vertically from a tall tree in the jungle. How hi 5y/re:n;:ywhfu q h)agh 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 d5hfw2,b9hq9 mqtw-(zxa o 8 2ovsvvj0own 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 frictio6 5 96xa-tlibu fr+pf5bsu 7gcnless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational potent 0od cyq (p.,az;.itsrz7gr ;tial ener0ctr.;idya pg qzz(;ors.,t7gy 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 of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platform wi khzx.ywfg767 th a speed of 5.0 m/s. z 7hkwfyg7.6x($\alpha)$ 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 s) zdsb/0bi+h0 l el,v5csd4okpring 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 a 0.30-k0/dils)+ vhd,zo5bls0c e4kbg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slidesvm. l0wyud i;, without friction along the looped track shown in Fig. 6–3l w0;uvyd,i m.9. 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 must it be released?    r

A block of mass m is attached to the end of a spring (spring ;6e-m4 bapyv*bua; rr stiffness constant k), Fig. 6–40. The blou evp *;ayar6 b-;rm4bck is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whose ;acjo+w 6lr :ounstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, ajocor: ;la6 w+ssuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 9q+ * jv*g fqx+yi1fnn1 where it is released from rest. Assuming ni*jnxq fgq+v +y*n9 1fo friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s atl fch ec8(zgb:k 7;8nngt)tpwz45j9n0 b0ibj 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 place n tz +.bz2f7k-jny*bid at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the zt *2bnyfnibz- 7k+.jtotal mass of the elevator and passengers.

  A cyclist intends to cycl0/rf0*;xqbf cn 6+o85yddbr.w wj 8gmc6o fboe 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 andn 9qbpnlq+z9: traveling 95km/h in opposite directions, collide head-on and come to rest. Ho+:pn9 qzbqln9 w much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child desc57jc+jqze3sv( ;jgcz 5t feq3ends a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this prq;7e t5 3zgqjc5 +csfj(zv3 ejocess?    J

  A ski starts from rest and slidegxv. nl pp48jt5g67jvs 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 ma 7-s/ p*huq ;q; yqs*oyn8fjabove 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 heiqa5ya. eyar6*ght of 1.5 mary5.y qa 6a*e.
(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 ;faj -cf41c4)hbl vl va floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speedvff1- ; 4 lchbv)ca4jl of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If the + f zhgi.u8c0+4m e6yjakxs;waverage force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled c+;+fj 68ku z isea0mg.4xyhw is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of pc0k. csw+4 paa 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 ve9ximpizbqyh,w4jm4j +thj +n3 /es 78ry 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 qjpjb /m4 h3tsy4 ,hw+m jn7zex9+ ii8stopping 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 liq: ,tyhp 7z5wpght horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it str:q,7 typhwz5 petch on its first swing?    m

  Early test flights for the space vlxj,m,a+q +xshuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h froma ,v +l,+jmxqx a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lif-kirm,wh 13s.holxe,3 fm 4.f dpgf7as)w dj*t a 315-kg piano to a sixth-story window 16.0 m above?f3jmw-a, swl*sd471h pdh) g ex f3im,.o .kfr    s

  If a car generates 18 hp when traveling at a scj/pg i3-sd ldtsc;; 4e/un u-:mmsjhg 5/hp 5teady 88km/h what must be the average force exerges;u5 ;phmpl/s5/h-tj 3c/jgnsc : 4ium-ddted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest z dr1wjb 9l: tb8.4mck+4bm izto 95km/h in 7.4 s. What is the average power del1jr+4z4 iczbdbb:.8k mt9lw mivered by the engine?$\approx$    hp

  (a) Show that one British yg-zzplj4 ,jdc6*z9 jhorsepower$ \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 -p4ku16ijqj.g q7m, d mlfrv)expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices thatxic rgc0n;j+cbj. /wt79x qi13qyz,t her 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to kee3,t9ni1zx qt/gx+jc y qj w0b;r7ci.cp the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-qshf9 v)t8l6 .7r5x l tjgf0qghp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg slhcu6;. .) nq.mtzdii r6b37yre ajz2hot from rest to 14m/s If this motion takes 1.5 s, what average rad)6l .27 m3y.nciith;r eqz.6b j uzpower was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute throughm2hy+nf9c 6u6o ) ieco a height of 3.60 m. What output rating (watts) should the pump motor h6 +yi9choefc n26umo )ave?    W

  During a workout, the football players at Statel4 r+9 gtpd2m7qtxe -lr.l 5 ixdxmk5/ U. ran up the stadium stairs in 66 s. The stairs mp5mqx/dr 2-4edit+ x5lxkl rlg97.tare 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 cyclist climb pzmx.ui** aefxm.gq17 /kc-b 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 poweufylb;2 loxr 7yawd34h1-w(wr output of 120 hp. How steep a hill can it climb at a constant speed ofaubx7hw;f( 3 yl41r 2lowyd-w 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 box alonpuc -1tlc*bb )5etbm (g a level floor at a speed of 1.2m/s if tm)15tt(c ucbp* bb -lehe coefficient of friction is 0.45?    hp

  A bicyclist coasts downn/e 04/sldf kg.gpev- a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that are desig12a m/1 em(w ufr ktth4jawn.g q;xz-:ned 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 at/rf 1zw 12k4w(.ghxa a ntm;:eu -jmq 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.v j22o32k bcaz3l(ly u0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, hcj 3ko3lba2v ul yz2(2ow 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 famoldd(7c-c p ,zn;ahi-4dbv ,ik 7et*ajus long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the7hjv4,p-n lz(,t7ac b* dk ei; cdad-i top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without obyaok8 hg*iq 87g5nng o8:d*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 the loop of rkgb8d *:qnhg y5o88 aog* n7ioadius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without hispjsxg (8je*:tw /f zo -jw,;yn parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. As oe xp,-/zygt;jswnj f:(8w*jsuming 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 horm,vpviv:. vwwb:g9o - izontal cord of length L whose other end is fixed (Fig. :bgw:po v,m vw vv9-.i6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-(/t.dj.3x onr(k6ncd zury e5high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calculate c .rne3d nj or(d(kxt6.u/5y z
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a huge spkf*w -pasjiyu0 -f-q5ring ($k=2.2\times10^{5} \mathrm{N/m}$) 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 9db1v 1 l(soffCalifornia claims that its lifts can move 47,000 people per hour. dvfs(f1 b1l9oIf 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 650kg/s and falls verticaae8z)cnv *y ;h 6/.n(pb dkzpbodr7z :lly 81 m before striking the turbink :eo)hvcd*n .by(/bd;rzp nzp8 za67 e blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a cir qndi m**7z)s nx/y fgg0gai,x(eje;e t*2-gl cular vertical loop (Fig. 6–44), the difference in your apparent weiexn*0 7mgdg -ggaze ij l,)y;*t*/esxqn(fi2ght 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 through it.    mg

  (a) If the human body could convert a- v pa/w/jar)m candy bar directly into work, how high could an 82-kg man climb a laddeva-majr /w/p )r 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 uqp.66ytzc5j4m1sao c 6mse8 59l6 hqm ulk*n fpward 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 bathroom scale, the spring inside the scale compresses 0.60 mxf7nn hh9e iyo3l884fm, and it tells you your weight is 710 N. lxfo7enf8hn4 8 9ih3yNow 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 over a hpbihk(+97v1 7x lx+ 0w h1a6t gnwftmlake (Fig. 6–45). He releases the rope when his vtg 1x 0tifxw971b+ahnwv7 kh hpm+ (6lelocity 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 ve. 3nc3 ab*d3uxxa 0s4vlhql0wrtical distance of 5.0 m in 9.0 s. What minimum*da3uwhb33 .sxqcna l0vx04l power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is5oqi/;xjl. 75ma uwq d pumped by reversible turbine pumps from a low to a high reser dqa7;o.u q5i/w5mlj xvoir. 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 cut in /8 fa4z ue dairrvs 7nc33z77ihalf. What is the spring stiffness constant for each of the t 8377 za4sficdr ri3ne /a7uvzwo resulting springs?   k

  A 6.0-kg block is pushed 8.0 m i3( 1g/o 0khqioor 6qhb+l08pg xg5hm 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 acc*8xetzh sq k9/elerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 5/x*qkz98seht 5km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for b9wvt s ,nzzg:501nqwcardiac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill iw5s0nzwzn:,g1b9qvt s 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-.:1 ll uni2xsakg rock vertically upward a distance of 500 m, what was its velocity when itl :lx1ui.2 asn 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 un2lxz*zm o4nkx7+p-m8pb)p ux lw. 4rate of 95kg/s (a) If this water wheel is set zp+umbpmn*2 n7x ll8okx .up44x)wz - 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