PH 105
Jones
Review #2
Spring 2013
Answers now available at end
1. A block of aluminum has weight 2.0N and density 2700 kg/m3. What fraction of the
block’s volume is submerged when the block floats in mercury (density 13,600 kg/m3)?
(a) 0.20
(b) 0.80
(c) 1.0
(d) 0.37
(e) 0.07
2. In a race down an inclined plane, which of the following shapes will win?
(a) a sphere (b) a hoop
(c) a solid disc
(d) the answer depends on the radius of the object
(e) the race will end in a tie.
3. An Atwood’s machine consists of masses m1 and m2 connected by a light string,
which passes over a pulley of mass M, radius R, and moment of inertia I. The tension in
the string connected to m1 is T1, while the tension in the other end of the string is
designated T2. If m2 > m1, what is the relation between T1 and T2?
(a) They are equal but not zero.
(b) They are both zero.
(c) T1 = m1g and T2 = m2g.
(d) T2 >T1, but (c) is not true.
(e) T1 > T2.
4. A man of weight W pushes down on the large end of a hydraulic lift. The area of the
large cylinder is 40 cm2, and that of the smaller cylinder is 2 cm2. If a weight of 40 N on
the small end will lift the man off the ground, what is his weight W?
(a) 3200 N
(b) 80 N
(c) 1.0 N
(d) 800 N
(e) 1600 N
5. A string is wrapped around a pulley that consists of a disc of mass 2 kg and radius 0.3
m. Hanging from the string is a mass m = 3 kg. What is the acceleration of the mass m?
(a) 6.6 m/s2
(b) 5.9 m/s2
(c) 12.0 m/s2 (d) 7.4 m/s2
(e) 2.4 m/s2
7. A flywheel rotates at 50 rad/s. It is brought to rest by a constant frictional torque in 10
seconds. Through what angle does it rotate during these 10 seconds?
(a) 5 rad
(b) 500 rad
(c) 0.2 rad
(d) 2500 rad
(e) 250 rad
8. A man of mass 80 kg stands on the edge of a playground carousel that is rotating at an
angular speed of 2.0 rad/s. The carousel has a moment of inertia of 1000 kg-m2, and a
radius of 3m. If he walks to the center of the carousel, what will the angular speed then
be?
(a) 2.0 rad/s (b) 3.4 rad/s (c) 1.2 rad/s (d) 2.5 rad/s (e) 0.0 rad/s
10. Which of the following is not conserved in nature?
(a) momentum
(b) angular momentum
(d) force
(e) all the above are conserved.
(c) energy
11. A U-shaped tube open at both ends contains a certain amount of mercury. When 10
cm of water is poured into one side of the tube, the mercury on the other side rises until
equilibrium is reached. How much higher is the mercury in the right column than the
mercury in the left column? Mercury has a density of 13,600 kg/m3.
15. If the gauge pressure of a gas is 3.0 atm, then the absolute pressure of the gas is
(a) 2.0 atm
(b) 3.0 atm
(c) 4.0 atm
(d) 6.0 atm
16. A hydraulic lift has pipes at each end with internal radii r1 = 0.01m, and r2 = 0.20m.
If 200N force is applied to the smaller end, what weight can be lifted by the larger end?
Both ends are at the same altitude.
(a) 10N
(b) 0.5N
(c) 4000N
(d) 80,000 N
20. An ice skater spins with an angular velocity of 2.0 s-1 with her arms outstretched.
Her moment of inertia is 12.0 kg-m2 in this position. When she pulls her arms in, her
moment of inertia is reduced to 6.0 kg-m2. What is the change in her kinetic energy
when she does this?
(a) 0.0 J
(b) 12 J
(c) -12 J
(d) 24 J
(e) -24 J
21. A block of mass 4 kg slides without friction at a speed of 5 m/s on a table until it
strikes and sticks to a mass of 6 kg. The two then slide together up an inclined,
frictionless plane. To what height H do the two rise?
H
(a) 0.51m
(b) 0.20m
(c) 0.74m
(d) 1.3m
(e) 0.89m
22. A cart of mass 3.0 moving to the right along a track at 3 m/s strikes a stationary cart
of mass 2.0 kg. After the collision, the second cart is moving to the right at 2 m/s. What
is the velocity of the heavier cart after the collision?
(a) 1.0 m/s to the left
(b) 1.0 m/s to the right
(c) 1.67 m/s to the right
(d) 2.5 m/s to the right
(e) 2.5 m/s to the left
23. A ball of mass m and speed v hits a vertical wall. In which of the following cases
will the ball deliver the greatest impulse to the wall?
(a)
(b)
(c)
(d)
(e)
The ball sticks to the wall
The ball hits the wall at an angle of 45o and bounces elastically off the wall.
The ball is moving horizontally when it hits the wall and bounces off elastically.
All three of these cases give the same impulse.
There is no impulse given to the wall.
24. An adjustable wrench is cut at the location of its center of mass as shown in the
figure. Which one of the pieces has the smaller mass?
(a) Piece A (b) Piece B
(c) Both have the same mass
(d) Impossible to determine without further information
25. The escape velocity from the earth’s surface is v.
What is the escape velocity from the surface of a planet with 2 times the mass and 4 times
the radius as earth?
(a) v
(b) 1.4 v
(c) 2v
(d) v/1.4
(e) v/2
26. If the earth were suddenly to expand to twice its current radius, without any change
in mass, what would happen to the orbital period of the moon? It would
(a)
(b)
(c)
(d)
(e)
increase by a factor of 4
Increase by factor of 2
decrease by factor of 2
decrease by factor of 4
stay the same
27. What is the acceleration due to gravity on a planet of mass 4.0 x 1024 kg and radius
8.0 x 106 m? The gravitational constant is G = 6.7 x 10-11 N-m2/kg2.
Answers
1a
2a
3d
4d
5d
6a
7e
8b
9a
10d
11: 0.74cm
12: 12.8 m/s2
13d
14d
15c
16d
17c
18c
19d
20d
21b
22c
23c
24b
25d
26e
27
4.17 m/s2