Unformatted text preview: Wt e9 1. The asteroid Geographos has a radius of 2.4 x 10‘4 times the earth's radius, and a
mass of 8.4 x 10‘12 that of the earth’s mass. How does the gravitational acceleration at its surface compare to the corresponding value of g on earth? a)2.4x10‘4g b)8.4x1o"2g‘ c)1.5x10"g d)3.5x10'3g
e) none of these
GmM Gm(8.4><10'12MEﬁm)m(8.4x10‘12)GMEarth _ Gco_ : F 2 i go os# _
w mgG mph (Rgeo)2 (24X10_4REanh)2 (2‘4X10—4)2(RE3”1‘)2 g Geographos = (8.4x10_]2) I: GMEmh (2.4><10“‘)2 (REanh)2]=1.5X10— gm memegélogqg 2. Tycho Brahe places a 6.0mIong steel rod on a rock so that one end is under a baby
moose weighing 2.0 kN. Mr. Brahe pushes down on the other end of the rod with a
force of 400 N. and the moose is held in the air at rest. The rock was a) 1.0 mvfrom the moose b) 5.0 m from the moose
c . m rom the person d) 6.0 m from the person 9) none of these Terriﬁed baby
moose l x I F.
l i I
TfLW = TCCW
Fl(6.0m—x) =mg(x) —> (400N)[6.0m —x) =(2000N)x
2400N  m  400N(x) = 2000N(x)
x =1.0m
3. The figure shows a planet in orbit around a star.
If its speeds at the four points shown are V5_ VB, VC, 0 and VD. respectively, then a)vA<v3<vc<v b)VA)VB>Vc>VD
VA>VB=D Vc d)VA<Vs=Vo<Vo
B Per Kepler’s 2"CI Law, the velocity of the planet will be greatest when it is closest
to the star, and least when at it's greatest distance. 4. The angular momentum about an axis through the center of a hoop (I = MR2) having
a mass of 2.0 kg and a diameter of 2.0 m which is rolling down an incline at 2.5 We is a) 20 kgm2i‘s w c) 8kgm2ls d) none of these iﬁl=1ai = MR2F1§3 = (2.0kg)(1.()m)2 =50kgm2/S 5. A Christmas ornament made from a thin hollow glass sphere hangs from a small
hook at its surface. it is observed to oscillate with a frequency of 2.50 Hz. What is the
radius of the ornament? The moment of inertia of a hollow shpere of mass M and radius R about a point on its edge is gMRZ. a) 0.68 cm b) 0.92 cm c) 1.84 cm d) 2.39 cm e) 3.98 cm g m6 f
3s 3(9.8m/52)
_ 20n2(2.50Hz)2 R = 0.0239 In 201:le = 6. Two straight inclined grooved tracks are lined up next to one another. Number 1
track is coated with a slippery film and number 2 track is not; otherwise. they are identical. Two steel balls are placed one on each track and released so that ball #1
slides down andw ball #2 rolls all the way. b) Ball #2 always wins
0) Bal 1 wins as often as ball #2 0) Both reach the bottom at the same time.
e) Insufﬁent information to answer. At the bottom of the ramp: mgh=13mvl2 —) vI : 2gh mgh = émvg + go): V2 must be less than Vl ! 7. A fisherman ﬁshing from a pier observes that the ﬂoat on his line bobs up and down,
taking 2.4 s to move from its hightest to its lowest point. He also estimates that the
distance between adjacent wave crests is 48 m. What is the speed of the waves going
past the pier? a) 3.0 mls b) 5.0 m/s d) 20 m/s e) 115 m/s v=7tf=§= 48m =10m/s
T 22.4s 8. The moment of inertia of a uniform rod about its center is given by I: ﬁML? What is the kinetic energy of a 120—cm rod with a mass of 450 g rotating about its center at
3.033151%? b) 0700 J c) 2.10 J d) 4.20 J e) 5.19 J
ilwz = l[iML2]u)2 = LU) 450kg(12m)2](3 6rad/s)2 = 0 3501
R01. 2 2 12 24 ' ‘ ‘ ‘ 9. In many cartoon shows, a character runs of a cliff, realizes his predicament and lets
out a scream. He continues to scream as he falls. If the physical situation is portrayed correctly, from the vantage point of an observer at the top of the cliff leaning over the
edge, the pitch of the scream should be a) higher than the original pitch and constant.
b) higher than the original pitch and increasing as he falls. lower than the original pitch and constant.
: d) )ower than the original pitch and decreasing as he falls.
It is impossible to predict.
The pitch will go down when the source is moving away, BUT, when falling off a
cliff (don’t try this at home), you will be accelerating due to gravity and so your
velocity will be constantly increasing. 10. When the mass of a simple pendulum is tripled, the time required for one complete
vibration _ _' creases by a factor of 2. b) increases by a factor of 3.
c) as not change. d) decreases to onethird of its original value.
'6 decreases to f of its original value.
The period, T, of a simple pendulum is independent of mass.
11. A projectile is shot from the surface of the Earth by means of a very powerful cannon. If the projectile reaches a height of 35,000 m above the Earth's surface, what
was the speed of the projectile when it left the cannon? a) 355 mis b) 505 m/s @827 mfs d) 710 mls e) 906 mls We begin by conserving energy! Eat surface : Eat max altitude
%mv2 — % = 0 ._ Mimi
(REalth) (REaith +11) 12. Two equal forces are applied to a door at the doorknob. The ﬁrst force is applied
perpendicular to the door; the second force is applied at 30° to the plane of the door.
Which force exerts the greater torque? ﬁe ﬁrst applied perpendicular to the door
b) the second applied at an angle 0) both exert equal nonzero torques
d) both exert zero torques
e) additional information is needed Torque is maximum when sin 9 = 90 ° . 13. A dumbbellshaped object is composed of two equal masses, m. which are
connected by a rod of negligible mass and length r. If I1 is the moment of inertia of this
object with respect to an axis passing through the center of the rod and perpendicular to
it and l2 is the moment of inertia with respect to an axis passing through one of the
masses we can say that a) I1 = Iz. b) I1 > I2. @h < [2. 01) There is no way to compare l1 and I2. I2 : mr
14. Curve A in the ﬁgure at right represents  n underdamped situation. an overdamped situation. 0) a moderately damped situation.
d) critical damping. e) a soaking wet situation 15. If head coach Randy Shannon were to say to President Shalala, "Either we spend a
lot more money on our football program to make it more competitive, or we should scrap
it altogether.”, he has committed which fallacy? a) the fallacy of division b the post hoc, ergo propter hoc fallacy
c) the domino fallacy e fallacy of the false choice e) the professional suicide falla 16. The ﬁgure shows 3 masses connected by light (assumed massless) rods. The origin of the coordinate system is at the center of the mass labeled A, and the Z axis is
perpendicular to the page. a) Calculate the moment of inertia about the X axis, and the force which would have to
be applied to mass C (the force is directed straight into the page) to give the system an
angular acceleration of 10 rad/32. 1x = mergc = (1.0kg)(4.0m)2 =16.0kg  m2 T : Ia = rF
PEI—a = (16.0kg  m2)(10rad/sz) :40N
r 4.0111 b) Calculate the moment of inertia about the Y axis, and the force which would have to
be applied to mass B (again. the force is directed straight into the page) to give the
system an angular acceleration of 1 rad/s2. 1y =mBr§B + mcrfm,B =(2.0kg)(3.0m)2 + (1.0kg)(3.0m)2 :27 kg m2
(27kgm2)(lrad/s)2 3.0m 0) Calculate the moment of inertia about the Z axis, and the force which would have to
be applied to mass C (the force is directed perpendicular to the 5.0 m leg of the triangle)
to give the system an angular acceleration of 5 radlsz. F: =9.0N IZ = merge =(1.0kg)(5.0m)2 + (2.0kg)(3.0m)2 =43.0kg  m2 1:=10L=rF F :12 = (43.0kg  m2)(5rad/sz) : 43N
r 5.0m 7:
17. An airatrack cart is attached to a spring and completes one oscillation every —s. 2
At t = 0, the cart is pulled in the +xdirection a distance of 0.50 m and released. (Hint: set your calculator to radians”) a) Write an equation that describes the motion of the cart (namely its position x as a
function of the time t). mﬁﬁlﬂsl
T T: —S 2
211st x : Acos(o)t) = (0.50m)005[?] =(0‘50m)cos(4tSl) b) What are the maximum velocity and acceleration of the cart? v = —A(osin (4t 8 '1) v =Am=(0.50m)[2—“] m T (0.50m)(4s—‘)=2.0m/s a = —Ac)2 cos(4ts“l)
am = A032 = (0.50m)(4s'1 )2 = sum/32 4
c) What are the position, velocity and acceleration of the cart at t = —Rs x = Acos((ot) = [0.50m)cos(4s'l ~t) = (0.50111)cos[45'l = —0.25m
V=—Ao)sin(o)t)=—(0.50m)(4s'l)sin[4s‘l i}s]=1.73m/s
a : —Ar.o2 cos(cot) = —(O.50m)(4s_l )2 cos[43_l = 4.0m/s2 ...
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 Spring '08
 Ashkenkai
 Physics

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