In what ways is the word “work” as used in everyday langua n( wjy9vf4l+q-kmjvd;, cjd3ge the same as that defined in physics? In 9 ;(k vvcjfwq,mdl3y j4 djn-+what ways is it different? Give examples of both.

Can a centripetal force ever do workkg +g4.mz6dfj+n e;xk on an object? Explain.

Can the normal force on an o dq-rn6g81ez.s u*dpj bject ever do work? Explain.

A woman swimming upstream is not moving web :+ tc, qnef(4+wwaw/jbr /with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on b(qtr :/bw wnj/w+eecf a4,+wher?

Is the work done by kinetic friction forces always negative? [Hint: Cons)ev*+atrrsv )ider what happens to the dishes when you pull a tablecloth out from under a*r))vrvet +s them.]

Why is it tiring to push h6 a0s7jpxuo8k ard against a solid wall even though you are doing no wo8 sua0jo76kpxrk?

You have two springs that are idkvzn1t 1 )a8bpentical except that spring l is stiffer than springn1tp z8 akb)1v 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 blocz:2j9v z6o1 6cnv,r1oqomarnk that is free to slide on a frictionless surface (Fig.6-30). The block starts fromq1 6ncv,26roavzr1o 9z:j o mn 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 potek d ov5fi+u si/ xc(45walgp12ntial energy change when you jump as high as yi4/ (coigp ka2x+wvfs5lu5 1 dou can?

In Fig. 6–31, water bx *ubg 06kspx v(ruw;:sxd6w 3alloons are tossed from the roof of a building, all with the same speed but with different launch angles. Which onu*xvb:p6k3xd6;srg w0(wx su e has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a *jqsc(4 vj/o3un2iw apoint that is a height h above its lowest point 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 tsw a4c *i(q 2njj3uvo/rajectory. 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 compress the spgj +ze*9 vwxp4ring by pressing down with your hand and then release it, can the spring leae4wjgx+v z *9pve the table? Explain, using the law of conservation of energy.

A bowling ball is hung fdv ,2osm4t)v7r4wqdfrom the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nosofmvqd2d tvsr47 4w, )e. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gr 2b+1*ogpr2d,qefr2llmcv 2 skxzc fut*e9: :avitational potential energy when water at the top of a waterfall fa*sg:e2kl+ ,poedc2 r ml 9q1: *uxz2r2tcvf fblls to the pool below?

Describe the energy transformations when a child hops around on a b5n lel2(mx+s*g,s he pogo stick.

Describe the energy d ;i,hn oix g-(dt(1ri;d,asn transformations that take place when a skier starts skiing down a odi,i( ;s h 1nx-d ;gi(rnd,tahill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total manlee6 xccmm f(6+;yu3ss m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there imxfnec 6yce;lmu3 6( +s friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their pat zycq*bv66n 2bh rather than stepping on top and jumping down on the other side. nbb*vqcy26 z6Explain.

Two identical arrows, one with twice the speed of the os xobql5cs --,*w /fxsther, are fired into a balews-xfo* /s5c lb -,xqs of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swingij-,vs87t z*bl-g lkuz ng pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to belg-7ju zk 8bv,s*-tzl wound up.

When a “superball” is dropped, can it rebound to a height greater than its origi9ego+w - l3k )cv:-q3u9ncd k;pz9 ibe.o ffgrnal heig3--up 3 owk.e 9v9k ) clngbqdrezi+f9o;:cfght? Explain.

Suppose you lift a suitc/v /9v19sl/ (sa cnme o)virsiase from 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/i 9) s1 /nrvsalmicsv(9 vo/e, and (d) the weight of the suitcase?

Repeat Question 22 for the power 6rpjjq:, vjf +0s0d gjneeded rather than the work.

Why is it easier to climb a mountain via a zigzag trail thanawq8*9cgss9 pi )8etmr/.sf p to climb straight up rsac.*/)ps pf99wms g8e t8iq?

Recall from Chapter 4, Example 4–14, that you can use a h3,4s.;ocz70o yeou4dlj qqxa b -0uppulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But yp,- e ldbjo;uq0aosqh7 zoc43 u4.0xfor 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 wh wnj puyxe;rkd36n9*/-a k) pden a 265-kg pile driver falls 2.x*6/pwd3 kj dnk 9npru aey;-)80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How muc , n4c n-bcpyqn xq*q*9*z1ohvun ;)mgh work is required?zn4m9)u *q,*;yncbog *1xn qpqnvch -    J

  A 1300-N crate rests on the floor. How much work is required to move it atn2po.8sylch u01;naqvm hq.6 constant speed (a) 4.0 m along the flnn;qc01hhy 2u vl am.8qs op6.oor 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 160-kg crapp8i2tc fblx633) cjete 10.3 m across a rough floor without a 6pxc32l 8i3e ptcj)fbcceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor aat cj64 v ivr4w9h.c9at a rate of for 7.0 s. Find the net work done on the boxvwv. 9acaji9 h44trc6.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a tab kt mptajoa.r.k.jpq /1 /1pw3le. How much work is required to.waq1 p3tmkpra1./ o kpjtj /. stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used toy3vre2nm+( vg liff objects we might not otherwise be able to liff. Shyv(mv+2g e3nr ow 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 d./v ro(rotlme4+0et3tn 0m(l7siol vb )d:sqown a 28° incline and is kept from accelerating by a man who is pushing 0it :dm(l /eq4+otmnls ltrv7bervo3()s. o0 back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an acceleration7hw xrq;4wzec- qer 18 of 0.10 g upx7 zrqhcwe 8-w4;req 1ward.    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 lir(rj pznrf.y58i, bao qyg))4near 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 theffsx;omhnj 49 v03bu1 x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move4os;juxn9h03 f m1bv f 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 exerted5h6aj : np,0x dfg ;shuju8,uv0 sj/do 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 molvu zne 0gai9hvw ocj13:x(2.yecule, 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 doubu1 uso ,+/kw- 1bp ny(+nvo-anhgrz* cled, 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 +8ezx 2 wm0ukr g9,:anyq.bqrto 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- f2(k*x/ jp m1au/vwczkgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exertq+ qu uyb8mtmr( 3ej89oz4 ds+s an average force of 110 N on the arro3uuz+(qr+ qsmyj tbo4em8 9 8dw 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 g;z22c-+ hjl (ytzod txlove backward 25 cm when the ball is caug ;o- 2(2tlh+yjz xcdtzht. What was the average force exerted by the ball on the glove?    N

If the speed of a car is mp0act*w-j njo o82s (e cg98alu( .waincreased by 50%, by what factor will its minimum braking distance be increased, assuming all 9(.accasop-el8oj*t nm8w wua( j0 2gelse is the same? Ignore the driver’s reaction time.

  At an accident scene on a level roat4v2p1ajjshn-7 e iq .d, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use thesjs-n v.aet71 j2q4ihpe 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 mzw3)/fls3kp t i) ;mc fln0eq1ass of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the ;qwtsf)lcl mk0 n)1/i3p3e f zdistance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if throwy 2;y wq s/sgjrp7df14n straight up by someone who does 80.0 J of work on it? Neglect air resistanc4 2wqfsp7dsrgy/j1; ye.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sing usd:b8cz)u qvw rh x4,yf.,h k66/imlle cable. Dete. m:uc/sfz6,vx4 kb6iw8y,) qhu hdl rrmine
(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, mgdd *z9aop61k, of 440N/m How much must this spring bedg6 9dp*a z1om stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higheraz9e: yst09 rha6aq : zqh6j;t. What is the change in potential enej ;:z:s9a a6e0 atq9yz6hrtqhrgy?    J

  By how much does the gravitational potential energy of a 64-kg pole v a5zi9nz8vppj,a3 x ex.o.er6 aulter change if his center of mass rises about 4.0 m dur 9i evoa,8.rx6.xejap3 pzzn5ing the jump?    J

  A 1200-kg car rolling on a horizontal surface has oc j6,1::;bcbzov 6ujxxz(wa speed v = 65 km/h when it strikes 6cx ,1jo bc:axb zzuo;jw(:v6a horizontal 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 mfdnp f7txh 93t8y-s,2.10-kg book from the ground so it is 2.20 m above the ground.9tf-mdty,hn 3xp7 8sf 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 top of a6xu)pigz :v01sni j* o 3300-m peak.0) gziuov nix6j p:1s*
(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 harftz0 gx pa5q.8pu9m5uo4- vvngs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end oz p5tqu.vf 5v8uo-4x a9prm0gf 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 ng; tdjlq439 yu6 v7ayvine hanging verti 4;gny 93y jlatuv67qdcally from 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, slid.qb suqljf 6l3crsi3jb2 efd*+-v ,: tes down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially my7l8 j6/ana jgiven a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed intj35guoj0d5 oc*sm4 bs o gravitational potential energy without the aid of a pole. With what minimum speed mustdcjosgus* m 40ojb 355 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 ver:-ygum43apgy tically upward from the top of a platform with a speed of 5.0 m/s. (ymga:p-34g uy $\alpha)$ 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 h1p)as6 kc3e(1yf tlu stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (as3( 1)keatlpc1 hufy 6) 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 without friction along the looped track shown in m-//tk vctrv8gxpir3 + lni-/ Fig. 6–39. If the block is to remain on the track, even at the top of th-vr i -rclktp+vt/xni//8 m3ge circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to t5/z snwl8z 87t)qn4 x-w pvcivhe end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial d7vv)wzp / wi-z8 n8tnq l45scxisplacement $x_0$ 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. Sz1g,i780v)impv*s ;po j xagh he is tied to a bungee cord whose unstret)g;jmogvxs* p7p8 a 0zhvi 1,iched length is 12 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 wh 7k.4y3m s((qltz,r/p yabtl kere it is released from rest. Assuming no friction, calculate the yms4p z a.kqyl7,tr(3/ (tb lkspeed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throw4:cdg5c2oe/ xeqdq 81n7 hpgon 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 a spfgd3+ q (oqg k9kp27crring 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 passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator 7 dgg qq+ 93o(prk2kcfand passengers.

  A cyclist intends to cyc3qb 2cj:b 8cjile 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 d(ld;9nup ,5yu wux/ 8vaqkr6jirections, collide head-on and come to rest. How much thermal energy is produced in this collision?p6k(j,uvx; q9l/n8wau5 udyr $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a sz:b yhve0lf znr 0*p*0w,x 7 yxsrg)a1lide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to frictir0 b0) y7epn0zx h,*vlxzs *:afw1 ygron was generated in this process?    J

  A ski starts from rest 5penwcre,0+d)z 0 wmnand slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the grounb e (guh +rs(2h*zt76y ,jvdidd.
(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 hex jjx62d77o h1l pss3fight of 1.5 m. j3phs s62 lxox177djf
(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 ac jc1 3(xbrhszi,5d5z 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 3( d51zxcibzr 5 hsjc,speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6 .w7*adf6:zeqdbr i1 b–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reaw a*.7dd:e r6i qbbz1fch point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 18.0 offcwd 8y *ox11o+, ym$^{\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 horizo 6uunv -xu1b-el(l/gsntal 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 stopping and turning back. What is the coefficient of kinetic friction between the block and the tn uluxug6-s-ve 1/l(b able?   

  A 280-g wood block is firmly attached to a very light horizontal spaweqkv ffq,xgg( 9f et)g b7x7g*5,xdm b10(pring, 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 i,(qtpfgefxdv7 b*fk)xg0e, 71 xagw bm9q5(gs 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 o(les/ ,rh7nd j87aqqi5km 7x w +jx)i n8(sbttf 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at nkje xw) 8s,qibars djm 7it 58xqn((t+7l7h/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 17s n(u9ktkm3n/50-W motor to lift a 315-kg piano to a sixth-story window 1m(unk9sktn 3 /6.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/ aj. ;-eaim3hr9, flit hb/,rsh what must be the average force exerted on the car due jl; 3i,.9as/br,ef tr-a himhto friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What isq3tqx3v90od7k u 9mi e the averagudx93ivotk937q0m q ee power delivered by the engine?$\approx$    hp

  (a) Show that one British hors6 r4e)o.r:u snjq8uxr epower$ \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 expforkryl/p,2 5o :(dqwressed 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 that her 1150-kg car slows down from6l)dqv vc3 k b4j0nuy+n/bq;8h.r rny to 65km/h in about 6.0 s on the levqu ;6bnhjdrqn)8 cv/kl ynr+ 0bv4y.3el 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- up(empbua-dzl a*:o qlf2 /*8hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a zlgqp/* f ka/d:;zsx97.3-kg shot from rest to 14m/s If this motion takes 1.5 s, whzqd:zk* g/ s9x/fpl;aat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water petv ;e0lu5j 5m9*qgdvvr minute through a height of 3.60 m. What outd v q 5j0mtv;leug9v*5put rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium d: 1u6y fy3:cclh;c/r(z t5jke(pii sstairs in 66 s. The stairs are 140 m long and inclined (c:i 15jrctf3yz(dk ; hp/c ui:ls ye6at 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 aod;(id+m8 koj2tq2r hyq dzg:r h0a3 ( 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a) ou/y8rv g:cvtt0r(y hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 N?y)orv (vu:8 rgty tc/0    $^{\circ} $

  What minimum horsepower must a motor have to be able ym0e7w5r m y(ito drag a 310-kg box along a level floor at a speye(7iy 5w0rm med of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dokcb7-j qgn )h5ped6i2wn 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) bu8bal9x8w 3 onpp3k bd2mpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up t832k a 9p8nbxw3lobd po 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 ykwq* dqw 63h7the first shelf is 10.0 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, how mucq 7hyd36wwk* qh 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 longg1gm.6( 1snflf r ar*n 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 traveling at 6.5m/s at the top of the arc? nm(.n l *f1gsg1farr6   m/s

  The block of mass m sliding without friction along t26c3* g6n* csgei2eeaax6 hrqhe looped track shown in Fig. 6–39 is to remain on the track *hegsaq6gxea6 *2e ir 3n c62cat 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 without his 47v/43, azmh q1j h rgknu8tklt14xfa parachute ope14nlr8ka / t 1mx3qz7,4kjftuv 4ghahning. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his 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 other end is 5**6w9qx p nn:( irmxeaqybd: fixed (Fig. 6–43).mr9:* yxwnb5 ai qq xpe:*d(6n
(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. Tfn:bhha0 + inx* n,7lyy rv95fhe climb is made in 5.0 h starting at an ei5:7vrnf ny 0+a9fh bhnyl,*xlevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above ax .9w0hxt q3g-e+3rrker p)if 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 nrar: j2g d1x jfd4(6rCalifornia claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) highenfr6j2:rdx 41ad jgr(r, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at f( :glr ckk()5 q/nepnthe rate of 650kg/s and falls vertically 81 m before striking the turbinkqnp(klg: n/ f 5cre)(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 circularzoh98 wccpg7( vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six w(c c phgo987ztimes 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 directly into work,u:1 sv ih9gcv5 how high could an 82-kg man climb a ladder iu cv v519si:ghf 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 q-78grwx 5kdcle 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 springt9fcuszi-fxs2x35 o * inside the scale compresses 0.60 mm, and it tells you your weight i5fi z txsu-*scx92of 3s 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 (Fig. dlizoti1l1+a wmk: * /6–45). He releases the rope when his velocito+ awid*/iz1ml k:1l ty 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 verticalct+7cg9n-rd(c 8uk r/ym hbz - distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this r/z7(c9 kc -h brnmd-8cuy+gt feat?    W

  Some electric-power companies use water to std7k :t j4v0dmwore energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store0twkv4 7 :dmjd 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. What is ti(df) -crk d5jv d;hi8(ovs( ahe spring stiffness constant for each of the two resulting springs?jd 8d(id;s)ok avci( f-vr 5(h   k

  A 6.0-kg block is pushed 8.0 m c/ fr+ (1bqimgup 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, g0 1q2rtx1e fshow long will it take to accelerate from 55km/h to 75km/h Assume the power stet 12fxr sgq10ays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks on oatisp6fe26/0)kv zxa ljqa77k7rrq6 -s .e nan inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the trea.7f a76 e6a 0-q7t6pkz jorv/rins)ka s2qlexdmill 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 spewsh kl4;,gc-tvspmz e2l2keo2 . a 500-kg rock vertically upward a distance of 500 m, what was its velocity when it lefcsek2o.-v ,2pgz 2 ;kleh4lmtt 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 2.90;(g-ezsrlkjtz) gj/afzcl6 i3. io0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is it)l g; kejorf9t cz-z6gs/3 ( .i0lzajis maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s