In what ways is the word “work” as useva*cc xvt2 au9 .skknp ,dvh)j/ 11)lrd in everyday language the same as that defined in physics? In wc 1.avx)rctv )j2 hnpk9a1/u d,kslv*hat ways is it different? Give examples of both.

Can a centripetal force ever do wo6kuy j 44)mnchrk on an object? Explain.

Can the normal force on an obje ya)mfal60 u*oct ever do work? Explain.

A woman swimming upstream is not moving with respect to the shoref/gv1/fa plp*1z 1 hvh. Is she doing any work? If she hpz1fvg1 apv*f h1 /l/stops swimming and merely floats, is work done on her?

Is the work done by kinet62m;ludiz35z (xzd ze ic friction forces always negative? [Hint: Consider what happe( ixzz e62m u;zzdd5l3ns to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wd jqws5 d+pcni y9(y1/all even though you are doing no wo ydn+( c5/9spywj i1dqrk?

You have two springs that are identical exclcrba)p/ a :dvds4x *.ept that spring l is stiffer than spring 2c)b xv.4spdla r:*da/ $(k_1>k_2).$ 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 iud(( rvqz,2 iis free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time rv (zdi2,uq( iit 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 jl 1t kdx1z2vxcr ek00:,t b3xchange when you jump30l c:jkbv1 tx1zr0kexx,d2 t as high as you can?

In Fig. 6–31, water balloc02zn4v wb5 oljbk8r.3ozi a;ons are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact?nio c5a;b.o0 2v3l4kj zwbrz8 Ignore air resistance.

A pendulum is launched from a point that is a height h aboveg3d7 bgl: .kzy its lowest point in two different ways (Fig. 6–32). During zd.gg :7lkyb 3both 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 tgb9pvan *f /p5 sq*46;xsl tpyable. If you compress the spring by pressing down with your hs pqf* ltngax5 y;/p4p6sb 9*vand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hunglxr 34 cln7q(e from the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against (x4lcle7q3rn his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potentia*6ivsmio 10qvfd4uk/l energy when water at the top of a waterfall falls*vv/6u 0q io kimd4sf1 to the pool below?

Describe the energy transformations when a cj* av*a9a:g ues2 vg0phild hops around on a pogo stick.

Describe the energy transformatir .pz*rs5rfg6 duasn36by;w(skm.y. ons that take place when a skier starts skiing down a hill, but after a time isym6 (gy3.ad.f ;brr*su.r wz 5sp6kns brought to rest by striking a snowdrift.

A child on a sled (t 1 b,tf j2/2dr.ctitk7z g8zc(ds l6bnotal mass m) starts from rest at the top of a hill of height h and slides down. Does the t sci28t/ddzf 7r b1k c(n.zl2,6tjgbvelocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in3u9 oj/ vjsr*bce6x c; their path rather than stepping onsjb3 *jv/rx6 uo 9cc;e top and jumping down on the other side. Explain.

Two identical arrows, one with twice the /ljmm+3dm;yqwu y:z. 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 z lm myyw+j;du3m:q. /penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a scno595s3*vinzv i 3g* j(mbhmimple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandf sg5(9minv3i * jn mh*3bcv5zoather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than idcciju)6a4:kjq*9r r3 5c zajts original heigjki3 a9qzjur: *4r56acccd j) ht? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on t1ce1j ql(jb(fhe 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 (d) the weight of the s(efqbl(j jc 11uitcase?

Repeat Question 22 for the power needed rather than the wr ,5o ksw0imf -5hl)s8sd vk:84bpazdork.

Why is it easier to climb a mountain via a zigzag trai.walc 6,nc +cgl than to climb straight ua6l,c ncwc. g+p?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to dekb/jzl7n (3sqcrease the force needed to raise a heavy load (see Fig. 6–34). Butknb7zs/(q l3j 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 gravitationawi: nyh xg5(t /-d05ukkz1hexl force when a 265-kg pile driver falls t/0nk5yxxu 1(khh 5d:g-wez i 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stair u) 0zk7,rpilithn)6ks 20.0 m high. How much work is reqrpn)l 7k0h i)ituk6 z,uired?    J

  A 1300-N crate rests on the floor. How much workdpfr/ 0 yei*g j1vhhi(*a,o5s is required to move it at constant5 o0*h dje1ys ,(vfhi*rag pi/ 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 crate 10.3 *(mr 1bjakx tsa lb1+x y(;w1gm across a rough floor without acceleration, if the effective coefficient of frict arb ykstm1 (glx;1+1a jw(b*xion was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a 110r8bflb* aqhmx4t2nso, egrate of for 7.0sr1e4h1toambq0, nxf*8 lb2g s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 k;d:nfj- *ns rs.d+ .7sm fdleig, lie flat on a table. How much work is required to stack th+e:-d7*n;f sl..sjrnid msf dem one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects yw- id358b gpvwe might not otherwise be able to lifgi-35 wv ypd8bf. 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° incline and is kvdc26 an4.d1cpywo (m ept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic frictio 2cm6o ywpnvd(d4a .1cn 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 acceleration oai-xw x0spqwb 6c5bp0 q. 2,qjf 0.10j0q2b .spqwwx5 - q0,bcx6 api g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the dis / 4sv;dg /n0/3 arlypmdlhp 7jo:3lkstance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shob9;a.3bol .kab 3tdl own in Fig. 6–37. Determine the w tlb.b3kda39 oa.b;loork done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts in the yv+m0/mjv4ee $+x$ 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 masqxnh 5w;+n )ots of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, c6 3rn.zoxuy5 iz/;uhgbm;8j7r mo4tby 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 st hpa+2 yepe)j9op 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 x.o1noi(0wwuawr e67buk, o + 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 average dj,c ; *kgmh,:th;lgtforce of 110 N on the arrow over a distance of 78 cm. What is the speed of the arg :d,hm*lgkct;, t j;hrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a f4hmlfpumpp/wb :h x 1i; cc/;,ielder’s glove backward 25 cm when the ball is caught. What wa/hpcp;c:bu 1 /mw 4xiflph;m,s the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor wi4+ 6g4/vcv jh60brof(pwrszg ll its minimum braking distance be increased,gvzr4v +pohrgw 64c0/ s6 bf(j assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a l g5f/fjnufcq-rye40rxlet./c; :b x ;evel 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 friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slamme.;f5xg0 ;//ec4fuxc:r lbyef-rq jtnd 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 reaches the pzuc)a4ncx3 f zx/x8-cuy 2uc4late, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resista2zuc -)xc 8n3 4xz4x/ycfucaunce during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock8f gu6853 c rg-o/bwmt1rat)mzmsco 4 go if thrown straight up by someone who does 80.0 J of work on it? Neglect air resistanceum5 3f4tmtw sagmor )gc1bcr/oz 8 -68.    m

  A 285-kg load is lifted 22.0 m vertically with an acce/ k(h3ny/v al).ou tmhleration by a single cabk/(yvml3 h/ua tn).h ole. Determine
(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 mp)lsh:9 l(oea uch must this spring be stretched to store 25 J of pote9e( )lsp:h aolntial energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher k w4f-nagd utub)2/y9 (1kadp. What is the changedftu1aa94y- p b k(/2wdnk)u g in potential energy?    J

  By how much does the gravitational pu3p* o)uh3mb hotential energy of a 64-kg pole vaulter change if his center of mass uho mbp3*h)u3 rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surfaef8yib c, -bz13re1x tce has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distayiec11-z3,efb8 tbrx nce of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from)w ybb (b5:jlmrdskl: g5f0o5 the ground so it is 2.20 m above the ground. What is the potential energy of the book r l dgrsobj)mybk:5wbf5(05:lelative 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 elz6l4os a7ighzej)- txv5 1s2bevation of 1600 m and climbs to the top of a 3300-m p7t4hv 6x) s esjzz5 ilg-ao1b2eak.
(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 the9zoxb1q -m xcx4-r fu- spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the sprin14 qzof9-uxb--x mrcx g, 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 haz ..h0*rq3hj9 v ,yz5omyb1ur lytbbs2btq 7,nging t5,byb.sl hur m j,o. qqvy9h bzy*1r2z 0b73tvertically 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, sl 7be/hwuh1mfgq 47pv*;7vdht ides 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 give v7)qyx- geix1n 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 ow)+6utuwo h-yex0o*energy is 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 2.10 m and cross thow*yh t+x06ou -w )oeue bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist juqw m(w:dat)xt8/ eow (mps vertically upward from the top of a platform with a speed of wqw)8:tw(otaed / ( xm5.0 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 (igb j ega0c*/:3q r e+yo0fdico0nore its mass), 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 0.30e ib0q+*og cfro a00e3yd :j/c-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 alongz4o( rw8s la -ck7/, wylzx2vc the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius iss7 o,y-/lv( 8azzlwkr 2 4ccxw r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a sp cjyof*;os8 7wring (spring stiffness constant k), Fig. 6–40. The block is given an initial disc*oos 87fyjw;placement $x_0$ 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 jump 9b73k;6vvi g yq.kgyss from a bridge. She is tied to a bungee 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, assuming Hooke’s law applies.9g7 36;bvqk.i kgs yvy $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in r7o6b7yo.4)p ac) l2uqqypg cFig. 6–41 is dragged up to point 1 where it is released7q2l467 cp.agrobq poy) y uc) from rest. 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 12y ,pp8romv a/4 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of antxtr/bgl+pg,a 6, ;pk 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. ; pt,a6px g k,gl/t+brLet M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up py1vqgg9ym6- 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 s45 wtqlpwq*ab2-g) wdirections, collide head-on and come to rest. How much thermal energy is produced inswqpaw l-wb *5)g4tq 2 this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m hiapchq: o29db- gh and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this proceo9:-d q bphca2ss?    J

  A ski starts from rest and slides k cli2/4sx2omq-e on a;)f k3h7n .qltdown 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 droppe i:rg6- prm;vez0f+ kad from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a hei;cm/x60v.a kgt 9axe/ -bq ykrght of 2.0 m, and it bounces back to a height of 1.5 m. q t0g xke;9ac a6y.k-//mvxbr
(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 with a constant4o-fjp n50j irwx7 4zn horizontal force of 350 N. For the first 15 0inw jr4 f7nxzpoj5 4-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 Figttp ci+6, x 06ukhhj6luf o6j /0auxt:. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth / xo06jx ti0caukt 6up,h:hjftl6u6 + 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 rnlwuwm8yns5c -y x/*z.7 5kt*op (+ nq +oqebleaches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal springaj zt)ig4 c/w- (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretcheg /c)aj-wz4its 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 hori*(we,py i z+bbqav y.5zontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm.+vypebb a,( *w qy.5iz 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/kszs1v : qk3xxm.jk ehl5gs1q2q 57oing 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) What would its landing speed have been in the aj57seqxq.vzk: m2x3 s hqklo5g1/ks 1 bsence 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-kgl4 *ei2by*cz v piano to a sixth-story window 16.0 m av*y*b l2czei 4bove?    s

  If a car generates 18 hp when traveling at g kjlucy9xg,44*zr;ea steady 88km/h what must be the average fzge *g xcuy44;k9r ,ljorce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. h0u;*d jcu5r+vu 8ey hWhat is the average power d;u *hcud+h8v0ejy5ur elivered by the engine?$\approx$    hp

  (a) Show that one Bri:xv:+is)7 t q( qz68;a xi+tfklgjlhvtish horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-h 4;gdri6nu ykui o ( jpap57bj/l,d2f.ours.”
(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 e 5;8xxty-pob( g cilr2ow .3acar slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (wl 5yi2(go ;x-8o3 .pwxaectbratts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do vphl h jw v+711c4pl0din 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelea yk1s 7q1uz ixc2(;tsrates a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average powkut(s 7qy12csiz1xa; er was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minu nal-euofu z 761gfsy4 ;b8tb-te through a height of 3.60 m. What output rating (watts) ubg- b4;o teza fn su6f1-l8y7should the pump motor have?    W

  During a workout, the fokw3e amb2c k ps6,t6p92+g ukaotball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined ct3 2psema+ k6uka2pgw 9k 6b,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 kig0/7n;unbz+)6(4 dnhgdr 5d vksaqa 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 maximuney0 zn ,.ten6 tyk0d/m power output of 120 hp. How steep a hill can it climbted0e ,6n ynn0yz k.t/ at a constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-;:ufjdhq2 6*fq m; obprs7miwr1pe, 8 kg box along a level floor at a speed of 1.2m/s if the coefficient of friction hespu 1j8*;rq27ip 6;fq,mromb w :fdis 0.45?    hp

  A bicyclist coasts down a 7.08- ne5m yyxbt/ $^{\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(8kmrssmqmr4y6o9i42; pvqt8h l 5/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 remains like an elastic spring up to that point, what must the effective spring stiffness c6 yi mq;4vorpql2sm85h9rts4 onstant 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 ef aft9p4 8jo,the first shelf is 10.0 cm off the ground, and the remaining four shelves are each e p4jf,9o8ta fspaced 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 much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fiv.0 5xw rij8yeob)2bzg. 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 tb2w0bv .8 xzr)yeoj5ihe arc?   m/s

  The block of mass m sliding without friction along the loopednzd+ 2)o81y ua+lr.ql3is+t xlv dk7 8vfp,ea track shown in Fig. 6–39 is to remain on the track at all times, even at the very top l.3yzxl)d,vk+f a 2so t ula7q1e8n8ird p+ v+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 wi*bct ck +9hm7 wq0syn)thout his parachute opening. He landed in a ymq07wk9sc)ch* t bn+ 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 71 tnam9p)z:ckv zj+ xm,mc1o0ba1f ba horizontal cord of length L whose other end is fixed (Figzca+oz mk1mvpm,1 cjxntb 019)a 7 bf:. 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 th4emx8+o+gfj0kso r 1a e top of a 3700-m-high mountain. The climb is made in 5.08o kr0o amf+xe1gs+j 4 h starting at an elevation 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 a huge springwo,4 caqu1 4.b9hao t)wxguu6 ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims tnmij;)pg)-y b hat its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (verticallin p;)gym)jb-y) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m befo kuyi2kb q0(4nre striking the turbin kn(u4kybi0 q2e 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 coasf xg4vr 4kt/r6aru 4+tter with a circular 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 times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’ttr t+4au4kr6 4v/xfr g depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a; kyln mm)b(lj.sf5: v candy bar directly into work, how high could an 82-kgmbk;f n:lmslyv j5( .) 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 fired zu *; 7b1 x:ic,(wjkx /gwqixlat 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 insid5 o l8uih/t8 v, tma*e)slr*eme the scale compresses 0.60 mm, mieltohs*/5*)l88tm , eav urand 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 5 a:h5p ad4t1zpuev.l 3m/s grabs a rope, and swings out over a lake (Fig. 6–45az .lvp14dht5 e3pu :a). He releases the 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 climbs a vertical fpo+b/eb ar y07:g+ivdistance of 5.0 m in 9.0 s. What minimum power output was used to accomv+yp 7aoi b/rbgf +e0:plish this feat?    W

  Some electric-power companies use water to store energy. Water iu7 6n .:lsgcl8kz+l5z ryt k/ps pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0c zruklz+6 l p/l:.7s58kt gyn hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stif k+0pgifk1,cas)+10owyhuatb7 x el8fness constant k is cut in half. What is the spring stiffness constant for each of the two resultingaki+hges +cytk 07, )ao1xw 018lpbuf springs?   k

  A 6.0-kg block is pushed 8.0 m up a ze,8tx5ooao.sr- 4k h 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 t/:-fgg) dv3o n ehvd;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 frictit;od/ h -fd3v:ggn ev)onal losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks on u y0ysv/d+ mu/an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at syyu0 u/+v d/man angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance of 500 u w2+i/+ kqm6s;z qd2c9qsrrdm, what was itszdsuw+m; is qq rr6qcd292k+/ velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a roi/k4k3 v/ rx2wlefps*gwojf; i k)(d75t c u.ate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum power outpjov*rg2ekwc;d5o t 4k s/ 7.3p)iwixfulfk/(ut?    W
(b) What is the speed of the water as it hits the wheel?    m/s