In what ways is the word “work” as used in everydd286s epc hfergz(y 30ay language the same as that defined in physics? In what ways is i3y8rze0 2(shged6 pcft different? Give examples of both.

Can a centripetal fo x:z5 2e1egg2*449 jhu-zrbpjovn tn lrce ever do work on an object? Explain.

Can the normal force on bc -+ 5bq)dgk, bocozo zm1se1v86w,e an object ever do work? Explain.

A woman swimming upstream is not moviz1r *9;w m.l- y69f6gjmq1es qow ylmong with respect to the shore. Is she doing any work? If shw-1mys; g 1ejyolm 6f*zq r9l qwo96.me stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [*4tvmg.:f 1ffq2xi xiHint: Consider what htxgif.4 i2v* f:mfx q1appens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wal 9k+ nxdii,dce ed.9e-l even though you are doing no work?ixncd-,ee9i9 dk+d e.

You have two springs that are identical/s8nl/a wes5lv sd57z except that spring l is stiffer than springa7//8els n5vs 5lw sdz 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 is glo;*: ocqr/oy/ w ,srfree to slide on a frictionless surfoq/wog rr, s*l:y co;/ace (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change when *i6 g6cjz bm5byou jump as high a6i5 cmb*bj6gz s you can?

In Fig. 6–31, water balloons are tosse 252zu sin.pj5tj0 oyed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance. z5n2ej5tjuo.y 0is 2p

A pendulum is launched from a point that is a height h above its lowest point insy+ h3 tp dyoi8()mez- two different ways (Fig. 6–32). During both launches, the pendulum is given an initial3)8m yhsez td(+ opy-i 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.l .xk 3zp,0)lrdtu)jk If you compress the spring by pressing down with your hand and then release it, ,0rlkj)3dxup zlk).tcan the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the heds69,s hnn2 ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ne96h2hnd ss,ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the grav h799 07pqt /lbzfbv+mb/gr ppitational potential energy when water at the top of a waterfall fallpbzt m bfg9p+r7p9qb//h0v l 7s to the pool below?

Describe the energy transformations when 0t rbn-c b w3w4e3rj.qhrb 0ycek2v of(0 .k.ja child hops around on a pogo stick.

Describe the energy tg-3zfc*u yug4ransformations that take place when a skier starts skiing down a hill, but after a time is brought to rest by strikg gyzu4-f* u3cing a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a.n. kfri(xx. u94tzmw hill of height h and slides down. Does the velocity at the bottoznr4kwxmf(i 9t.x u..m 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 step over a fallen log in their piu 2+rs p69uxxath rather than stepping on top and jumping down on the other side. Exxr6s+up9xu i2 plain.

Two identical arrows, one with twice the speed of the other, are fired into a s ev6en8a36 mibale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrowsm6avi68ene3 ? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) ignorink(f by /a7 qg7fld:b1r;xuw0xz)ctk(0 y; mkqg friction, and (b) taking friction into account. Explain why a grandfather clock has 1 (yxf0/xu f)0 l( ;cqgyb ;kkawmbz:7r ktdq7to be wound up.

When a “superball” is dropped, can it rebound to a height greater ejzioy)6 4hc( than its original height? Ex)ycohj4z 6i( eplain.

Suppose you lift a suitcase from 2wcz3q nbrgs4vd* )l,the 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) the height of the table, and (3qr)*bg, wclzs2 vn4 dd) the weight of the suitcase?

Repeat Question 22 for the power needed rather 9(zl8yx1mm rgthan the work.

Why is it easier to climb a mountain via a zigzag trail than to cliqmnll, *hc g *bp*4m:go3b2msmb straight u*bl*hplms b4m3 gc*o g,mn: 2qp?

Recall from Chapter );0re9ksoy no fd6l1pnj+kn. w6+g tg4, Example 4–14, that you can use a pulley and ropes 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 energyktlyn.)jwr+o0g efo ;+d9n16sk n g 6p concepts.

  How much work is done by the gozwdpqz2d ;k4l,:x5 l ravitational force when a 265-kg pile driver falls 2.80 m p2 klwzzx5,ql: ;d4do?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work ijgl3y8u c.w9 a+wb v 0xhn(-pns requic awn b0p3n+yh8j(.w-l g9vuxred?    J

  A 1300-N crate rests on the floor. How much work is required tostx3o)bxn+ jga( ixde6v x99, move it at constant s oja+()e tx39i dgn6 xvbx,9sxpeed (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 a ln;7a (gccgi7 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficgc 77il ;acng(ient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force a0ut3 p*y -ahcncross a floor at a rate of for 7.0 s. Find -3nu*a 0ptychthe net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How mucvoh5 .nenotye;:er--1f/ w stv o6n /zh work is required to stack them one s/; :nfoz.-e5w 16nt-y/htoevonv r eon top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liffv-hxg0 );tt)zqzw)4z emtb/i objects we might not otherwise be able to liff. Show that the ratio of o-v/)t)z4tbxi0; gh)qwz tze mutput 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° incl/ rtk;p;*e 9g) ssmk +9eloagfine and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective/egsals;99 t+eofm; k r gpk*) 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 c j tvxj,4l;h1j;s ,sba helicopter of mass M an acceleration of 0.10 g upwarcj,,s4jx1j l;bvhs;t d.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is linear and that4dc8 b xu /- ujwzbx8el gm)p).7f9hdt $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as showyf9;ge09 go zs,b4tk on in Fig. 6–37. Determine the work doogzf,9s;9egb0 y4to k ne 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 h df,nz/+v d;ofr4p0s on a particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen m6nze q.ks.y y+olecule, 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 iel2,u26 alr nns doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elect) f;g+s5 zhj/hm3yueyh x26qx ron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 (d;ay vr )xqh+t, a)dgw0er ecy(fn0*done to stop a 1250-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 ehx/uy jnp t4:;m8f1aa8s8 geaverage force of 110 N on the arrow over a distance o8/g 4s1ene py8t auxf8jm:;haf 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s mb*4p*/w. dv tr kc1 g4glav2meoves a fielder’s glove backward 25 cm when the ball is caught. e4.v *tlar dvgb4mg 21c k/w*pWhat was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what fac2*j qxej.fz/mxli c*5 f he1ago./y5mtor will its minimum braking distance be increased, assuming all else is the same? y mf5*hg/ f. jx ex51mojaq.2 lcez*/iIgnore the driver’s reaction time.

  At an accident scene on a lev9)te2 g4pi-jb bv4 spuel road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic fripb-j)4v us ig9te2p4bction 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 it reache 2aut. +t-seurs the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, esr +.attu-2u if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up bus lk rp-(os8y8c(6q fy someone who does 80.0 J of work on it? Neglect air resis8por u((sly8q6 s-c fktance.    m

  A 285-kg load is lifted 22* 6mo787u )u3kz rgbzxp,rw uk.0 m vertically with an acceleration by a single cable. Detezmkx 68u b)p u 3*7rgwuko7rz,rmine
(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 must this sprin t2 z/)vnmgj/sy7 l4i9mazm,wg be stretched to store 25 J of potentiamv7 4ta/9sym jz2nz )/ilm,wgl energy?    m

  A 7.0-kg monkey swings from one branch to anoth6+s h 9l:n;y9t))pitiblfezw er 1.2 m higher. What is the change in h:ilsb9 i etn tz+6l)wf;p) 9ypotential energy?    J

  By how much does the gravitational potential ener nd:pa en pk:gy/:4n/sgy of a 64-kg pole vaulter change if hinnd n y/eaks:pgp::4/s center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horiz bpo6,o1 ,,pq:4dcbq,z +ej4dkm nvd contal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a diodnp:m4+cb kz1 cd p6q e,,bjq4,dov,stance 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 book0dn 2h-fm liy7 from the ground so it is 2.20 m above the ground. What isym02 hl- nfdi7 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 t)5 5nj;laxmtrop of a 3300-m peal;ta5rjm n x)5k.
(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 vertt g3 bm((*aa((hr4w kbxhcgjd/rou /z 6w;lg2ically next to a ruler. The end of the spring is next to tt6omc w4gu(/2l;( wbr*ag(k 3raxb hhz/ jgd(he 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end 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 hasqx 9,giz-fzd +x-,.mfftf;znging vertically from a tal+s. -g; ffxx,dzzm-f,9q zftil 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 frictirh y92/f)jv ihonless 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 friction.goh3o-uf 8bpz;ek.4k :cvojless 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 kincj 5jhi,uk3j. etic energy is transformed into gravitational potenti3kj.hu jc5 i,jal 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 of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertical *3oeivh/ivn,y94c qb ly upward from the top of a platform with /hnivec vy 9qio,*b43a speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its ajimml8 sqe;y3, 5my ;02gu8h b. tgaqmass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball whgu8; ;ltmjq 3msi2abq g,8hay0yem 5.en released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the loopyo-e)9h2 xoy*u2xwzm ed track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what meo-ox ) wyz*xm2y9h 2uinimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring xi9*1i +o+lbgha. whdc*y*k m stiffness constant k), Fig. 6–40. The block is b widmx*+ga9.yc hh+*i kl1 *ogiven 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. rp/d*;hmtkon0d)vkev oc/-58;yx hh She is tied to a bungee cord whose unstretched length is 125 0o rhdt/ho;*x-kvh ne;kv dc/mp)y8 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 where i*p3ii k8 2i+ngeu1jckt is released from rest. Assuming no fricc+ u1i8j nikk eip*2g3tion, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throw/mhhhn(::b ctwa s3x3n with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing aego ;mf2f p:kiw2k u6r4v8i gi6:y5wq spring to be placed 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 passenggfyo8k42kqfrwi e i wm5:g;uv p:62 6iers 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 e: wqbmoa ta hb*6j*2+cycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg a xqp2ah8ggncftm/ys;a6 h 74;nd traveling 95km/h in opposite directions, collide head-on andm pc6gnqgha;y;h4t8 2a7xs/f come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m si m//-t1n83kewn whnhigh and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this prowi/n/w8 nhn stem3k-1cess?    J

  A ski starts from rest and slides downuw*ovq28sy(ito9 t w 9 a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the grounwmei-7mf;hf,wza 6g 8 d.
(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:: 2a zntr1qjw back to a height of 1.5 m.1j: na2wtzqr:
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor witu)9o r cgi1xzp n*y0,m gm8s)mh 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 speed z 9x,y*1mg)iu cnosrpg8m0 m) of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passe91fv5fnk2z 7 o/dogwns point 1 with a speed of If the average force of friction is equal to onez 15knofn2fgw do7/9v -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 reaches the foot of a stzllenh6pyiub cw88 /z8. 0l1teady 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 spring (k=1vhr5eo /f3q. /nh.mzxhmqik7y.yt 11y ./wq k80N/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 beyondz.x1m .5oyk7qh/y3w h1 ..fmynt/iqk e /hq rv 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 fiwox/- : ncjzq.rmly attached to a very light horizontal spring, Fig. 6–40. The block can slw -x nqc.j/:zoide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg includ (68k2n6 maxzkn1b lvqing pil mvnz1qb26kn( l86ka xot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air 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-kg p)mp)f r vk9.gziano to a sixth-story windowzm.)rkvp9 )fg 16.0 m above?    s

  If a car generates 18 hp when traveling r 6xhihrbr)/+ow7 .*d+yqjrzd c 4ff* at a steady 88km/h what must be the averagr4fhc zbd. wh+)d7o/ifj+y* r qx*6rre force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car acc8l 88enkou1 etelerates from rest to 95km/h in 7.4 s. What is the average power delivered by the enu 8ke88n1t leogine?$\approx$    hp

  (a) Show that one British horsepor6vj dfz7,j;3pnoij .wer$ \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+jgy-t q1so g1 “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 6.cifzdp b sbd7490ok( 00 mpyr5km/h in about 6.0 s on the level when it is in neutral. Approximately 4bf0 pdd sir7c omp 0(0kbyz9.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 3zolbx2f- 7uh 4-brknmotor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg s +x) ivo;c/4srxfsm 49qne hg7hot from rest to 14m/s If this motion takes 1.5 s, what average power4qrf sgnhic+m4 );o9/exvs x7 was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a heig 4x dc(q,p,ufzht of 3.60 m. What output rating (watts) should the pump motor hu ,(xq,fzdc 4pave?    W

  During a workout, the football players at Sta y k v fm4,pjurorovc(b5/:)g(te U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclinem) b vukj prr:/fo,5g(4ovy(cd 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 a 6jp s6za+d*hzub aaai ):47 8li.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hill)*oo ndu* ql,-cb2f :zzf. iev can it climb at a constant speed of 75km/h if the frictnb fcf:)- zi vu*,d*oql .eoz2ional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower musti)v2 :mnzzuh + a motor have to be able to drag a 310-kg box along a level floor at a +z)h mu: z2nvispeed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7z1szct):j;p)x *( cpsuq:(wi 5y wiwn.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) bns4p),jcmu+ww 77l ( et.nca pumpers” 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 lik 4twa cj(pn.n,mc7w7p) lu+see an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, ank.y6 mh7dbj,(awt/ c /2zg tyhd 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 shy,t6z7ag2 wc.d m h(b/ ytkh/jelf 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 fk )tp3vui53 6hxb5nyf4)cs d famous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling5ni)fyb5 upk)3x 6vth fs4dc3 at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the lm.fiff94) aszy6wvz* ooped track shown in Fig. 6–39 is to y6f si4av 9zw.fzf *)mremain on the track 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 jumping from an aircraft withoudqa:r lb/-brcf3z9y9 t his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and rql:bzd9ab9/ y rf -3chis 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 whoseuad.8edpj l h.nn pa 3u4v,z7( other end is fixed (Fig. 6–4347v.8upn ad (pj3 .lzudh ea,n).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The clim(vnrg5eh.rw ,n .j8t7 by b7nnb is made in 5.0 h starting at an rn hy. (nw jtb78.v5b,7negnrelevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable brea5b) s3 rphpgc5xmz8 5sks when a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California clai -koft5f 6vjd1ms that its lifts can move 47,000 people per hour. If the averag-jk fdtv61 o5fe 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 fewao, dex0bj6h. woe1ba2gowy* ;+z0alls vertically 81 m before striking the turbih0y,+we*1o20ob gbdw6xzo e j.e aa;w ne blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. bz* +thn2 nic2v:9xlp6–44), 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 siz nc*:vph22zb n 9x+tlie of the loop or how fast you go through it.    mg

  (a) If the human body cot0ebf0 249xukt)f 7 gb-6oaa1ws* n5kyz ie pxuld convert a candy bar directly into work, how high could an 82-kg man climb away a9 )tk t-b 6ipex2ue*f 7o410nzkf5b0 sxg ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward ang)i6+qwgeszvz g6k4nt3,4a x ule 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 izv28lsh u0fg/ui 00pohl-)bknside the scale compresses 0.60 mm, anduv/20)hs8zfi g uh pk00 ll-ob it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake/ld;w pbl7+: * vln56lzcvxm s (Fig. 6–45). He releases tv+ v:m5ls6b wxp;n lzl/d7*lc he rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete clirs wnrm qsl5g 11;2h(kmbs a vertical distance of 5.0 m in 9.0 s. What minimum p5rq g;11nwh2 s( smrklower output was used to accomplish this feat?    W

  Some electric-power companies use watevi3vu7at)yzc; 3 spa) r to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir)it c3as)uv ;y 73pavz. 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 half. Wh.iben5wi (q 46sh9ux tat is the spring stiffw eisi(qnh 4xtu.9 b56ness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 x /0jax9x;p+rfix p :jonf3a+m 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 55km/h in 3.2 s, how//huwvb* wt *g long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frvw/ u b**/twghictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient e,2ko.;g:i.pjavl2i hbkdx -ji .-xkwalks on an inclined treadmill (Fig. 6–46). Estimate the power requikij-x ka.bi p.h2;lojxv: 2i,ed.-kgred 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 vers3)q*keo 1l pftically upward a distance of 500 m, what was its velocity when it leftps1 *e 3qfolk) 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 wagdc f7oe*g(74 n9 ohyrter wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is g 7c 4oy(dgf9*hr7eno 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