In what ways is the word “wot6:gl chv9; y 4ij6jn;qv 9xsnrk” as used in everyday language the same as that defined in physics? In what ways is it different? Give examples y4g9 lvnhj6; t9v;j :6xqsi ncof both.

Can a centripetal force ever do work on an object? Explainh:eakpl3 j;thm-bzfs ku1,ix a * b+*9.

Can the normal force on an object ever do work? Explainf5xl ptown4 /rw* h, .hdw7dnddg0v89(jt :cf.

A woman swimming upstream is not moving with respect to the s-5s v 61vkeqtzhore. Is she doing any work? If she stops swimming and merely t- evz v61q5ksfloats, is work done on her?

Is the work done by kinetic friction forces always d*argp(*rfa,pk p+5l negative? [Hint: Consider what happens to the dishes when you pull a tablecloth o*l(a+p*fr g , 5apdprkut from under them.]

Why is it tiring to push hard aglqih.*:erqare. 8 q(hainst a solid wall even though you are doing no workh8qa e(e r*rl:.hq .qi?

You have two springs that are identical except that springo dt.+ 5tjt,xk l is stiffer than spri+. ,k dtojt5xtng 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 horizonta /tlhv* 65w5r)aeed rjl force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, etv*r5a jw)e5hrl/d 6 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 much6d9y*kg dygx u4-.c hrtif3d0 does your gravitational potential energy change when you jump as high gi*rkfdg3hdyxc4 tdu- 6.y0 9as you can?

In Fig. 6–31, water balloons are tossed from the roof of a buildi8pc.kt ;xpltpdk6 o 16ng, all with the same speed but with different launch angles. Which o; xtdo 1p.8k6 l6cpptkne has the highest speed on impact? Ignore air resistance.

A pendulum is launched jsk.vak i 7t,(bds*r8aa+s8 i from a point that is a height h above its lowest point in two different ways (Fig. 6–32). Duds(kaaka b* j7vtsr 8s+ 8ii,.ring both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If,bnm w rwdx4)* you compress the spring by pressing down with your hand andmb *w )nwxd,4r then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a 1+g6rpbu 7 yxisteel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his1ryp+ ui6b7g x nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational pozecr6 x e.3ok57 lt/zvtential energy when water at the top of a waterfalrvxt3 5 7.ok6 zzeelc/l falls to the pool below?

Describe the energy transformations when a child hlb n5pp3 zpnh439og,cops around on a pogo stick.

Describe the energy traende 1f h.,jh.nsformations that take place when a skier starts skiing down a hill, but after a time is brought to rest by striki1n, h.fe.hjedng a snowdrift.

A child on a sled (total mass m) ss.dro7( lbv kz)i7y chr4y9c0tarts 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 is friction 4 yiy.o7ch 7(kcbvl9dz rs0)r(deep snow)?

Seasoned hikers prefer to step over a fall (jnr3g tls/o;en log in their path rather than stepping on top and jumping lst j/ngo;3(r down on the other side. Explain.

Two identical arrows, one with twice the . b2(enw*gcay speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how(c.b nyw2ge*a much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, im+yr* rau5/iu *j1w:x0 kl hz(a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound 1 xi az0rlwki*u:yu/+5 h*rjm up.

When a “superball” is dropped, can it 7 d3r+x7/4ep2j 9zgsbifnyl0sy4 rvt0uqx2 s rebound to a height greater than its original height? Explain.7 g+p00 xsb /rj4ylzsuqei3fr 2ds 7 n2xv49yt

Suppose you lift a suitcase from the floe /457y iqvd/o5h7bo tyh+uql or 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 itqu hlq hy7be 5/dtv+o475yio/ takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather94ht/ ufh-;x9qztp t z than the work.

Why is it easier to cli e3 rpk0f2qgapawwcs 3 5acnn/3l g5:3mb a mountain via a zigzag trail than to climb straight ucwr 5apsc3e:/g5ln 03w3 2f qg3kpanap?

Recall from Chapter 4, Exazzo 4:oxiz7ppjt/u bly)15 c 8mple 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fjoxpz8 z/)l1i4ut pcy5zob :7ig. 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 8 n.g l,ypytkaae4lkwa3 ;t66265-kg pile driver falls 2.80 m? ptkk a 346yl. ;6gn8a, tayelw   J

  A 65.0-kg firefighter climbs a flight4n/i 734alps,,wvc91nsje rap xx5b q of stairs 20.0 m high. How much work is requiredxssc7bqen1rj p/ a5v 394lix ,pn ,4aw?    J

  A 1300-N crate rests on tppknj* kq+8): 3t 5cthjgf sc/he floor. How much work is required to move it at constat tk:jpkj g8nhf+c3cs*)p5/q nt speed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg cra;;2nylsphpgk/ol m:*te 10.3 m across a rough floor without acceleratioo s *p;k/ylnm2;ghpl :n, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floyjm(gg4zb( *.kg/w)c(xhdz oor at a rate of for 7.0 s. Find the net work donyd zob g4(.(/jzxm )w*kg ch(ge on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table 5tw34w:re-6rv zs hkk. How much work is rw 5-:k 4e6 wvtzs3khrrequired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff os/yzu 2o4gf;objects we might not otherwise be able t2g zos4yof ;/uo liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incx- phu1n6qfg* line and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient -* fpxugn hq16of 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 accpqwh)f;bfat -q8 39,m1pqipk eleration of 0.10 g upwardqp1iwktamqpbf f 8 9h;q)-,p3.    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 thad fk z8u,tjx:u. 1udc9t $d_{\mathrm{A}}=10.0$ 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 objec9;cm5ync *fuhsa yzo 64k/m+ mqh*8mut, acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 10 m +oc/un5uf *9km y;h8 m *4zcmash 6ymq   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 particlejvh9om(m,v: z acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with mass y7/hj:dvxon- r:: bbqof $5.31\times10^{-26}$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, vlw;w y:b53/nt5 bmw2 n 9nzctby 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 requirelp/ tp8 n3:bkvd 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-kgcar traveling at0d0hsxgn 9-td:lw *u t 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an a tob+3z:. lup2+mmdkhverage force of 110 N on the arrow over a distance of 78opd +mzk:b 2+t.ulmh 3 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelin- muh4rejwlkf8+ td*s0.c ;ing 32m/s moves a fielder’s glove backward 25 cm when the ball is caug in-+rd4fh; w.lcst0mj e*k8uht. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, m3xj2p30/ /bp8 (u pk)miec)roh jzydby what factor will its minimum braking distance be increased, assuming all else isp jcye(3k/)pdzjmhm38r 2 u0o x)bp i/ the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators me1k6-yurd k4dlmlb szgv/5,) k asure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and tvlskbm1r k ud/d5g-l6)yz k,4he 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 a pq3wqa 34e.uht By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimqua4q3e h w3p.ate 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 if thrown str 9x8,dxqkgp:rj4y wmy*n2v7laight up by someone who does 80.0 J of work on it? Neglect air resistanckr y:* vdj xy2x94 mqnglp78,we.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by ae1 q7mgc(vvq8,h ar,yk )e j,p single cable. Determiy)gehe ,7pjvamr ,q cvk8(q,1ne
(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 ml4juy5t2ig z *uch must this spring be stretched to store 25 J of poteu yl4z5t2 ji*gntial energy?    m

  A 7.0-kg monkey swings ftfe 3t: 9)fr6yi.gsz bj9y5 lzrom one branch to another 1.2 m higher. What is the change in potb)zl y9js.5t zt9:fy3e6 rgifential energy?    J

  By how much does the gran*dxlvl zxc d3+f (vm47)gn (uvitational potential energy of a 64-kg pole vaulter change if * v m3zx7 (4 lnldgfv)cndu+x(his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling oc/ 3*wz+ k;hxcpi+wcy n a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the springcy*+;pw x3c+hkci wz / stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.sqk.dw , vjj4;8.wjoc20 m above the ground. What j.wv j .wc4okdsj;q,8 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 tz- n6jfmp ai(v y3x(j(op of a 3300-m peak. jy6x-3(anp zjfi ( vm(
(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 the spriidh 2*lj7s2 g*k0u,ag-jx hbm ng is next to the 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 thj,* 2*lgh-dgsu7 hjibak0 mx2e ruler marks?    cm

  Jane, looking for Tarzan, is runnivq :7n*rdar m1:na c4ang at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high ca :rr4*:nn ad7 ac1vmqan 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 fri3nni7 xchs0 z4ctionless 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 xyj/l s61b:gn b+)ps sfrictionless 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 ycviojwpwh4+ j 77euwny7qj 7 8 7xd9 b2hav41is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10ww8i7 yjv4aov 4b 7h7e jq+u y771whnxd2 c9pj m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artisba0nw2iu8 rs+g7s- xv t jumps vertically upward from the top of a platform with a spsaixn r+sgu802b 7wv -eed 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 rdn a)ev(8 d(rits mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwarda( d)rv(d8enr 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 shownotq,m k 5p.b1e in Fig. 6–39. If the block is to remain on the t1 q5bmtep ,k.orack, 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 g 20jq-sp4m8x(sefcothe end of a spring (spring stiffness constant k), Fig. 6–40. The bloc0o-2ec q84sfgm(jxp sk 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 bu xx0xoz(6j.xungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assum6oxx u(. j0zxxing 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 i:-ctk9zv + l2nfc0 jlyq9nfa:s dragged up to point 1 where it is released from resttavny -nff+c:2: ll9kq 9 jzc0. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 1qxv v5e bqz/;5nn:m p72 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 spri b+51j a/1yjc2cvpsa cng 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 toyj /2cacbsj1 p15+v cap of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a cg r1 +q6b9sbnu j+c+y7.8 $^{\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 o +xcy 9 n602pmmcr6qrtlrm-y+pposite directions, collide head-on and come to rest. How much thermal energy is produced in t2m +0+n9l6cy m x-c rt6rpqmyrhis collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descend* ank m7kh pv 0;3j7y-ga okh)yu6d7kds a slide 3.5 m high and reaches the bottom with a speed y*7 a6v7uhja0hp gdkmkyo -knk;d )37of 2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and sliw 7ichz2 d).+tehxj 6p nlvb+2des 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 grpx9+uop w ;c ije4z/0qound.
(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 he5 (5+aonbj, n fml+giyight of 2.0 m, and it bounces back to a height of 1.5 m. lfn+o b(i5 5ymg+ja n,
(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 gym61*xyxr1g dpw8 t lih6(m1 rest, is pulled across a floor with a constant horizontal force of 350 N. For t8rg*6y i ymwtmh x(l1g1dx61 phe 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 of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a sp :c qwllybc2f/ s68 j1ton7z7zeed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach 71tzzl n lcqo/ cbsw 78:jyf62point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steaf q(( 3/wuodblt7boh y uo,4 )aso71bug wjd.-dy 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 rcan b6(i:t1a2;tdh tspring (k=180N/m) as shown in Fig. 6–40. It is noted that the blockc 1a2(tt6;ntria bhd :–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 table?   

  A 280-g wood block is firmly attached to a very light horizontal sprin /sc6vp3 yaj.x/h:(u hk4frctg, Fig. 6–40. The block can slide along a table where the coefficient of frih(/hct k 3 .p rsjax4/y6fv:ucction 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 in.2xne69v6dej**a nlyvb7c x t cluding pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) y nexbl9vad*j2 v*ec67n.tx 6What 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 piano to a sixth-s zeme*v n,mx6*tory window 16.0 m abovnz*mmxee6 , *ve?    s

  If a car generates 18 hp when trasdb)(z*qy3t:cb;qgqik3 ab2y; + mqxveling at a steady 88km/h what must be the average force exerted on the car due tbqxm+;3 dsqa:b);z igcq 3y2q*b( ktyo friction and air resistance?    N

  A 1400-kg sports car 2*mjf07xf)boc0 l cgraccelerates from rest to 95km/h in 7.4 s. What is the averagef 0 *mxc0frg bo72jc)l power delivered by the engine?$\approx$    hp

  (a) Show that one British horsepower4wr m8x*jjisc;x : i6 ujli(/m$ \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 “kilowatt-hou b4pebvq4vku)69ao p, rs.”
(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 towro- ht4ak0+7hl5,om, 8ttj7k**ky izdsn k r 65km/h in about 6.0 s on the tikhk8zrmto7k-7 w40o5d, syj*at r +k* ln,hlevel 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 30llv g*qiykqxhss. c-a/ne** o -ys,6.0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest 9b l7w.2alhfr to 14m/s If this motion takes 1.5 s, what wa2br9l h.l7 faverage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What 3 kcdxe0go ot:60xm)gout0k)gte cd3x 6: x0ogomput rating (watts) should the pump motor have?    W

  During a workout, the footbwvkwy.ca t3.d 0c4: ruall players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and intcud.4k w3a. c0vyw:rclined 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 avsz3n 0p,ep8whmh h5. 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 maxig:lt7so/)5kc mvcr-qmum power output of 120 hp. How steep a hill can it climb at a constant c-tc7sgvl: /) omqkr 5speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able bh +,g2g f- l4sk2d1 ca)bdtpoto drag a 310-kg box along a level floor at a p b2k -dbtsgc4 ,f)1lao +2dhgspeed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dwblc ed50 far46 ij*j0own 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 “5miasy.t p 1ckbp+i6)c9z /h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remainsz1+.t kyps)p6c9i abc like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the remaina1k-r4w 6ugza77i w7e sxssa,ing four shelves are each spaced 30 1 zeus,4767xw- ikgraw ss7aa.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famsdu)w,d-:tpu z2f7ur ous 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 th)uu72uf pt, :-dwr zsde 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 friction along the looped8xk02 vmjeeh y 8w9/eacrp8 ,ln)w 5jl track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the ljr8vj ew0wm lx92 lec a8,p8he)y5 k/noop 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 paracv,)wchfm5 kd.bwm p)27k ih h9hute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minoh5.mkb)d,kw )i hc2vwp7 9fmh r 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 horizo5 ihrzc4.ouax3cp7m 2s ui6q+jv:x0 jntal cord of length L whose other end is fixed (Fixva 6hu 43cm7:rpcsji0qoz2+x u i.j5g. 6–43).
(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-a (bma h;r mdk0d.iu uy32d /sm.vrj++m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. C+/av2ymbd.(um. +s 3dmdi;khr0u r aj alculate
(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-kg5 wb34 isndvz, 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 Californdb m7ct3k -ev.ia claims that its lifts can move 47,000 people per hour. If the ave.e t73bvk-cmdrage 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 ve wro-hx-.xy8:n2eb mjrtically 81 m before strik.nw bo2mj-x- 8xhr y:eing the turbine 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. 6–44), thhgw1nqjv)l 48 1n.f((na j fbne difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go thro)nnv q4a . fhf1gn(8nj1ljb(wugh it.    mg

  (a) If the human body could convert a candy bar directly into work, hajisn1m+2 r2isf9 l g.ow high could an 82-kggr2i+l.n2sf 9sa1jim man climb a 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 firedpdau 7ea30l8*ie occ , at an upward 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 uo:)+f*jtezhzoh7c +g4h( oq0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at itoo4h ()o :fghu+*e7zzcq tjh+s peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over d9caof6vx4tzf,/ k-ep t1( cva lake (Fig. 6–45). He releases th-p9ftc a,f6 (vvd4ktz/ceo 1x e 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, afq9e8s +z3l h s9y,bjk 72-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was usfq 3lzhb8j ,9s+yes9ked to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped bmg -cdy9: xj+oy reversible turbine pumps from a low to a high reservoir. To store the energy produc cmd:- jyx+o9ged 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;j5 )r9fopkuh0r8z r i is cut in half. What is the spring stiffness constant for each of the two resulting springzr9rp 0juh5i;f8r)k os?   k

  A 6.0-kg block is pushed 8.0 m up a )kf8+9-cpt d1j bahvw 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 acceleraqloum 1zk0 -x;a*ef,.ft b(lyte from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losse0fl1mel;f .(q-zoya u*b ,ktx s.    s

  In a common test for cardiac function (the “fs4f l/.7lr1 a9hpd ztstress test”), the patient walks on an inclined treadmill (Filarhz7ffp sl9. t41/dg. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward d sb,o :rc.9j0ted3:dirmb2 r a distance of 500 m, what was its velocity when it left the o3.d brrbdsr:d: c9jm,0ti2 evolcano? $\approx$    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 fromtuy, .m-nms+p a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to ,ysm+ mt .p-nuprovide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s