In what ways is the word “work” as used in everydei q nqam.qt5a3i8 fx:8wg* 9fay language the same as that defined in physics? In what ways is it different? Give examples ofgfqnf iq*9w: ma8 8 qti5.3eax both.

Can a centripetal force5a b6;w6ptrcvu( 58ywx+f vx l ever do work on an object? Explain.

Can the normal force on an objectx 9,(v e ql3o4.7;n ljcklij;6ac vfrf ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doing l gg(j6ful +;d3pjd3 sany work? If she stops swimming and mer(d;+ll g j33udf jpsg6ely floats, is work done on her?

Is the work done by kinetic fricti+78zmgyxoa, wfb6 s b u4te4ksjhp-0+on forces always negative? [Hint: Consider what happens to the dishes when you pull a tpj+ 8,buas04 tz4 f6m g+wks bxe7hyo-ablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you anc; flkqbz4o4 quu+n. p 0jf2+re doing no wu lcfkb0zfn+4. j;+ u4qo2pnqork?

You have two springs that are identical except that spring l is stiffely8+ 2( l dni)d+tksder than sprindk( i+)8d+ se nld2lytg 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is f xype/,f:)t j.emntc :ree to slide on a frictionless surfac : xe:/y.mpt tj),encfe (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change when sqj ; l(hgob)kpi 5/j(you jump as high as you chps5ojk (;(gbi /l) qjan?

In Fig. 6–31, water balloons are tossed frowrc(- hpmc 9enu: y/.zm the roof of a building, all with the same speed but wy.nhpr c9zm e-/:uw (cith different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest poi-(q9ync zve+v)be: /tn,ow1a vcc d j+nt 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(+q1/evy,-9n z )nbeacjct:vdov+c w 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 you compress the spzj g2 qj(da y9yccog 6-h/0q7wring by pressing down with your hand and th0z6ogjcd7 w9 y-ayqj2/(qg chen 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 steel wire (Fig. 6–33). The ink ;6tp i kdltfew, -f .84tfa3mszx4u(structor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing(k d3l 6tszetw pt-auimxff 4k;,84 .f it. Why?

What happens to the gravitatp y 67lm0mhism mf0z,7ional potential energy when water at the top of a wa 7hlmmfyz 7sp, 00m6miterfall falls to the pool below?

Describe the energy transformations when a child-iui lvg3u t9, hops around on a pogo stick.

Describe the energy transformations that take pc4z6zq0p3 qa place when a skier starts skiing down a hill, but after a time is brought to rest by striking apq36z0 4cpqa z snowdrift.

A child on a sled (total mass m)gou09* f+v7f1*tpx4 rparczgv v5c.j 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) i5g gtr1u*p+c j*rf4av9xo. 70c vzpfvt is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a frx g37kmi nl87allen log in their path rather than stepping on top and jumping down on th g387mrlnix7ke other side. Explain.

Two identical arrows, one with twice the speed oxuii 2a:cdj/ ye(obyzx9*z57 f the other, are fired into a bale of hay. Assuming the hay exerts a constant fric e:ciyzx* ydojiu9a 752b x/z(tional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in tmd k(d;ed xz:d: kr7-oerms of energy, (a) ignoring friction, and ( d d;kz7(d:kmx der:o-b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” i0 odw 0trob0k0s dropped, can it rebound to a height greater than its original he0rw0ok 0o bt0dight? Explain.

Suppose you lift a suitca cdhfdohwfbg,*0v3 l4-)oj n(se from the floor to a table. The work you do on the suitcaseovf3gbod *dnf, 0)-4 hjhlc(w 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 suitcase?

Repeat Question 22 for the power needed t3-ho -/sck*izbdll.rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to cls)y0*nucvu 1 uimb straight unsyuu1*u0 v)cp?

Recall from Chapter 4, Example 4–14, th cpzj79hk3ygj*wf41oat you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope *pc hfy1 749jk3owgjz must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fal)xlfkd**/*yvzg v9v hls 2.80 m? hvx*vzd9) l*k*gf/y v   J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How (gvjuzqi, h*eb2 uu*ls4;g/j much work is requzu* v;2she4 juuq*ilg(jgb/, ired?    J

  A 1300-N crate rests on the floor. How k5dr1y*bgh d/uy /up5much work is required to move it at constant speed (a) 4.0 m along th5dr */kd1/u pg buy5yhe 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 cr3s m9x09rtw ogzei(( pate 10.3 m across a rough floor without acceleration, if the effective coeffswt9 39 0oi( zr(gpemxicient of friction was 0.50?    J

  A box of mass 5.0 kgva7;+u,qhsijvvh ee(0 sz (v 5 is accelerated by a force across a floor at a rate of for 7.0 s. Find th+a ;ejsvi eqv7vz v((u0 ,h5hse net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How m 3 nhnz 8afti5z5hl;8jk)8kuj uch work is required to stack tz3ku5afh z;88)8 tklj5 nihjnhem one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff obje62vfb .jzi e;nbgj- t5cts we might not otherwise be able to liff. Show that the ratio of output force, bit6 jv2-.z ;jfen5gb$F_{\mathrm{O}}$, 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 kept from accelerating bf h* ehlf/ fj00nzxv6xu5z m;0 i :9j8wmx:jsfy a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kn xse m*9;: jfz0zwfhv0i j8lxf05j6 ufhx:m/ inetic 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 helicopterq -zmc3i 4cqa4 of mass M an acceleration of 0.10 g upward. 4m q3i c-4acqz   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 af up6mmio(7,z xis 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 axi4as: e kph5* 7v u;zk-;fgbedvs, 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 = 1z su-k5gevvf; *;bhad4epk:7 0 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 t ywt;w2xy,)non 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 molecule, with mass +etmn+ x cz,t0of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by ljnyxzo8zd :08i9;ac 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 reqb6y hoo-gxy/toeo*78uired 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 at 105km/hl-6x0 ys iupa8?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110iy9e:t5bkoh3 mfo:4 u N on the arrow over a distance of 78 cm. What is the speed of the arrow as it 9 yotk:b3: fm5ueoih4leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm w)z;9piq 7i5 pi:39dku cmb8lpw kv (dghen the ball is cauwi vkup78q5;9bi c dp3pg:)l9diz(k mght. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increas 3z tgibr (-9vdoh+qy/ed by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s r /vt+- ogzi(9y bhrqd3eaction time.

  At an accident scene on a leveamiu y l69n/*mf1dwtb;yb 68sl road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the *ysn8b6i6 mf9l uwyb 1;tdm/acoefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reach)tm3fin uc rxlmvkk;k(- bl 2n8y31h )es the plate, it may have slowed by 10%. Neglecting grailytm r cf)2n)x k8 l3m kbvu1-h;(3knvity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does cosxe,/q hh). 80.0 J of work on it? Neglect air resisx e,och/ hs.)qtance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratioktspo1xp auv2fdt6 r)++);unn by a single cable. Determi1;x uvudakst)o2n)+rp6t +f p ne
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much mustc1. fc .pj*-pfiflf*t this spring be stretched to store 25 J of poten1cflp.f.p ti fc*-*jftial energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m hix gsc)j+ ;t7*h0qnf(xjgjs n. gher. What is the change in pots nfhxqsxjt.7+cjgg 0( )j*n;ential energy?    J

  By how much does the gravitae9c+ .30llc bywflt7 stional potential energy of a 64-kg pole vaulter changf97 3.etlwsll0 c +byce if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h ;k 8kw;tgbk3v7mys u: when it strikes a ho;83: swkv;tk ukbg y7mrizontal 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 lijn1v9 x53a*az; grul afts a 2.10-kg book from the ground so it is 2.20 m above the ground. What ix3jv uaal*r a951gn; zs 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 top6bgx.(8bbb iiwdm d4zgvj 05. of a 3300-m peak0 i(zbw8d .g vgx5d6bib4b jm..
(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 next6xk,ni v hwx:6 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 of the spring, where will the endi6vhxx kw ,n6: of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running 2(pypqtwng 7g eo-. 2mat top speed (5.3m/s) and grabs a vine hanging verticae 7no.m(gqgpt2 y2p-wlly 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, stari4./x 8 ydvj 9 df5k3vrfivx4)*wlwhkting from rest, slides 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 given a shovqemhf95if +k9bx( y4je 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 into g: rx3r(q3prq dravitational 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 the bar with a speedrd3 rxrpq3(:q of 0.7m/s.    m/s

  A 65-kg trampoline artist jumpjw gbywl;7x(2s vertically upward from the top of a platform with a ylwb7wjx(g2; speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness cok pba2( )mxej+nstant is 950N/m is attached to a table and is compressed down 0.150 m. (a) Whmkpbja+x (2) eat 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 tra2 x3ocz6d m(of,rvat: kx0y+ wck shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h mustmtxoz,r0+xwcd f aky2vo63:( it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness conloe+rmva :rxo l 0mhstz850)3stant k), Fig.3 or+vxz: 0ehal 8mt )5l0mors 6–40. The block 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 m/4vaansspxc rvu q/.0 i+43d 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, assxsa/.vi mv3 0urs aqp/+ 4d4cnuming 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 18 y wsy52;ijfp where it is released from rest. Assuming no fric2 jf8i5;wpsyy tion, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle ob+2h eb yvq7g/f 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 an ele ,lti79 7fiz2ghm5 gjkvator 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 brou5ii f7kmg7gt, 2h9jzlght to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cy, nadtr7lrc0kswm 63 xd;,4l vcle 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 ofm6adjm 4 z dwh4p*sgq:4(1imu mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and comep w ui4 sq4*mh61j4mga(d: mzd to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slqdm,n5je1y s11w/2r em psg2nide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generydw njs122p5gme q1re,m ns1/ ated in this process?    J

  A ski starts from rest and slides .e2wcwm 3 c lb ;gs9la0onm6zs:lu/e6down 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 abovehoxh rg g:65+chq2 xt2 the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of:;h9 * hpx9h/ra.. p maovm*nry qj/tt 1.5 m. rarh9x p*/.j h/ynt9po .avtmm h;: *q
(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 adob7kw(bpj pkx)s 9 br;t.9)r constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next jb b.spp)rw xdk;7r9t bk(o)9 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 speed of q8 of r.6h0u.bxh+fcy:v f:uf If the average force of friction is equal to one-fifth of its weight, :ff+..vy :80fxchq 6o ubfhurwith what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 184yh7has )bl 2uxf94tj .0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring (k=18jj qhgfz:q kkyk3+kk23 h55(j0N/m) as shown in Fig. 6–40. It is noted that the f 5k:3j kj(g y+q2jh5 3hzkkkqblock–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 horizo layau/qx7j upc ,x:.:ntal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of.ax: yqua : /jc7p,uxl 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 6wum9n/ r1 femspace shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200kw 1/e9u6fn rmmm/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-)m+0*xjdd0 dz n0 aeymW motor to lift a 315-kg piano to a sixth-story windd*mzan+m0d) 00xe dyjow 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must03eqj,hnr(x hj(qeoafwqul *c5425v dr0d ; h be the average force exerthj d4x0,3ur*0(jawef5; qr qqvoeh(h d2l5 nced on the car due to friction and air resistance?    N

  A 1400-kg sports car accelera;ygrbms6 .fy- n fo:6ktes from rest to 95km/h in 7.4 s. What is the average power delive6f6o-kfm. :sy grb;ynred by the engine?$\approx$    hp

  (a) Show that one British 2, fd5 v9de1udnr+ mmghorsepower$ \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 ozc4vn9r -5 euhften expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that h8 z8-ag pqmhwh;or0tu;) qb7 ner 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 7 wqr8-gzt;b) mhao8pq u0hn7;5km/h.    hp

  How much work can a 3.0tykxj 5t-pdd+ d(v6*5k e hq(t-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot fi( o)e /tt 81ak8at,nuh;bsxvrom rest to 14m/s If this motion takes 1.5 s, what average power was8ei hatkt)ob v/;t,8 (usxa n1 developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height o0*z / omj+edvyv clq3:f 3.60 m. What output rating (watts) should th0do/ v vlq :*m3zcejy+e pump motor have?    W

  During a workout, the football players at St7hn lcl8d: i xmkeht)0rl;2yfo *5k3y ate U. ran up the stadium stairs in 66 s. The stairs l3 y0h :dk;l5kc2iom8efrylh 7x)t n*are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist clc(; aebfiqnjw(uq : y:n9z,m(/)ti ohimb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power outpr qqwcwblstg d22t *d l0kggjl,p;/4+/v o q.4ut of 120 hp. How steep a hill can it climb at a constant spwb4gqo kg2+*t /q; s2d0wrjptl/l.dg l4cq v,eed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to e iy 29y+whvez/p7(y mbe able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coe79yyzvey h2 w+e/( pimfficient of friction is 0.45?    hp

  A bicyclist coasts down) jquhz*5:cddr2eee 5 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 car:paz ikai67 8k/+c icis have built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds 8iki7+zi:p c6i/a kca below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has 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 fi9 k0s./x u(4 4ansmz wqyazr5irst 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 shw0 a zym/ zasnk9(xris4.q 4u5elf 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 (Fig. 6–42) inod v2/t, xv0rvvatl(r55.kg k the 1936 Olympics shows that his center of mass rose 1.1 m from lauvv,dx5kvktg5o . a (t2rvrl0/nch 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?   m/s

  The block of mass m sliding without friction along th7ef2my4( mr+zhbkbuux 13 8c ee looped track shown in Fig. 6–39 is to re zmxfbkurcem b7y 21e38u( 4h+main on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without hi7gy0d2 c 9 dik2skd:wps parachute opening. He landed in a snowbank, 2 70pc2dyi k9ds: gkwdcreating 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 dws* t:idte17 5 ux9au1e/bh+u,eqxr end is fixed (Fig. 6–43). he:q51 7uxdebustu+ e91dia *wx/rt,
(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 0gih /3ap e+skd6c mp)the top of a 3700-m-high mountain. The climb is made in 5.0 h starti/3 pi+d kgsc a)6phm0eng 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 qif 1xetd7r(; 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 Cajrf ;-sar12q-w3q3pii0g11 kzsxmkh o.;jqnlifornia claims that its lifts can move 47,000 people per hour. If the average lift carries people about 2f0xqi pn 1sg 1r-z kjh .j1iao3k2rwmqq;-;s300 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 vertically 8+e mndfk2j99 e0 i2i q3)dtvkt1 m before striking the turbine blades. Calculate 9ke0km) d2+nv3d2tfij e9 qi t
(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), the dffz-uvz 1s 7e*ifference 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 tfzsfze* 7 -uv1he loop or how fast you go through it.    mg

  (a) If the human body could convert a can;x:o 0mdlxaps ) *8onndy bar directly into work, how high could an 82-kg man c oxpnx*l )0 o;as8mn:dlimb 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 at an uj *xxc5* gk2hk/h et va8kjk)2pward 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 bathros,;mvlr 1bfe v7u*gmpap c63;om scale, the spring inside the scale compresses 0.60 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 its pe b rp vcu*v1 efg3mpasm;l6,;7ak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a07m 3;yfllpodwn 9f dc xyg1;d6n gj5to5c:h + lake (Fig. 6–45). He releases the rope when his velocity is zero. ll9x0:c1 d7pt3m y;nwnod ojgyf hfg65d;c+5
(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 e l,o;cbxeymdktjoj ,49047u climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accoxdm4 7ej ob yeutcl4,k,jo90;mplish this feat?    W

  Some electric-power companies use water to store energy. Water isw*44/drs j7mj 8 npod7ty2 b.ko- sxbw pumped by reversible turbine pumps from a low to a high reservoir. To store theskn /*rw4 dypx7 4 ts.m8jo7-2jbo dwb 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 the springi )f,l0ct 0fe1dj,) mh ge+uwi stiffnee)i0u) 0 e,,flfg dmwci hjt+1ss constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up awslm f;i 88f25*nlmwf 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 3zlp5hx8kap t6y85g+ o .2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the poyk x658a5+lg8 phopzt wer stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (k n:ka 6h3ejj9the “stress test”), the patient walks on an inclinejk:e3haj k9n6 d treadmill (Fig. 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 r1rq,yi1y8dc; 8ybkw aawnp 2- ock vertically upward a distance of 500 m, what was its velocity yr18k,yanw- 1 a2w;cpbyd iq8when 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 heigh7 ys6u bvnaq;9t of 2.0 m at a rate of 95kg/s (a) If this water wheel is qsa v6yn79;buset up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s