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Physics 201, Final Exam, Fall 2006
PRACTICE EXAMINATION
Answer Key
The next three problems refer to the following situation:
Two masses, m 1 and m 2 , m 1 > m 2 , are suspended by a massless rope over a pulley (disk)
of mass mP and radius rP. ( / 2
2 I = mP r P ) At time t = 0, the masses are released from
rest.
- The tensions T 1 (in the segment of rope attached to m 1 ) and T 2 (in the segment of rope
attached to m 2 ) are related by
a. T 1 < T 2
b. T 1 = T 2
c. T 1 > T 2
- What is the initial acceleration, a , of m 1 (take down as the positive direction)?
a.
p
m m a g m
b. a = ( m 1 (^)! m 2 ) g
c.
2 1 2
m p a g m m
d. a =
2 ( m 1! m 2 )
mp + 2 m 1 + 2 m 2
g
e. 2
m p a = g
m 2
mP
m 1
- In terms of the acceleration, a , what is the work, W , done on the pulley for the
period t = 0 to t = t 1?
a. W = m p
a
2
2
t 1
2
b. 1 2 2 1
p
m m W at m
c. W = m 1 (^) arp
The next two problems refer to the following situation
A string is wrapped around a disk of radius R (I=1/2 MR
2 ) that sits on a frictionless
incline with angle θ as shown. The string is pulled up the plane with tension T in such a
way that it unwinds without slipping from the disk and the disk rolls without slipping
down the incline.
- What is the linear acceleration, a , of the disk down the plane?
a. a = 2 3 g sin!
b. a = 3 2 g sin!
c. a = 1 2 g sin!
d. a = 5 3 g sin!
e. a = g tan!
T
θ
M
- How much work, W , must be done in decreasing the radius to rf above?
a. W = 96.1 J
b. W = 227 J
c. W = 340 J
d. W = 480 J
e. W = 546 J
- If someone now sprinkled sand on the table (causing friction) and it was observed that
the angular momentum of the block decreased to 3.9 kg m
2 /s over the first 0.5 seconds,
what is the average torque, τ avg , on the block over that time?
a. τ avg = 0.18 N m
b. τ avg = 0.80 N m
c. τ avg = 1.6 N m
The following problem is all by itself
- A pitcher throws a ball past a stationary batter. If the ball has no spin and is
thrown straight, then the ball has no angular momentum with respect to the batter.
(T) True
(F) False
The following problem is all by itself
- A rotating object necessarily has a net torque on it.
(T) True
(F) False
The following problem is all by itself
- A rotating object necessarily has a net force on it.
(T) True
(F) False
The following two problems refer to the situation described below:
A block of mass 5 kg is placed on top of a block of mass 10 kg, which in turn sits
on a frictionless horizontal surface, as shown in the figure. A force F = 98 N is
applied to the 10 kg block, and the 5 kg block is held in place by a string attached
to the wall. The coefficient of friction between the two blocks is 0.15.
- What is the tension in the string?
(a) 45.0 N
(b) 7.35 N
(c) 0 N
(d) 27.2 N
(e) 55.7 N
- What is the acceleration of the 10 kg block?
(a) 2.72 m/s
2
(b) 9.06 m/s
2
(c) 19.06 m/s
2
(d) 3.42 m/s
2
(e) 1.56 m/s
2
The following problem is all by itself
- If you double the amplitude of a simple harmonic oscillator, the period of the
oscillator
(a) decreases by a factor of 2
(b) decreases by a factor of √ 2
(c) does not change
(d) increases by a factor of √ 2
(e) increases by a factor of 2
The following problem is all by itself
- What would be the natural oscillation period of a 30 kg child on a swing
whose seat is 3.2 m below the bar from which the chains of the sear are attached?
(a) 5.5 s
(b) 6.28 s
(c) 1 s
(d) 3.14 sec
(e) 3.6 s
- Refer to the points A-D marked in the figure below. At which of those points is the
pressure maximum?
A. Point A
B. Point B
C. Point C
D. Point D
E. Pressure is the same at all four of those points
- The pressure on the roof of a tall building is 0.985 x 10
5 Pa and the pressure on the
ground is 1.000 x 10
5 Pa. The density of air is 1.29 kg/m
3
. What is the height of the
building?
A. 100 m B. 118 m
C. 135 m
D. 114 m
E. None of the above
- Refer to the figure below. What can you conclude about pressure P in the bulb and
the atmospheric pressure P 0? (The tube is filled with mercury with density ρHg)
A. P < P 0
B. P = P 0
C. P = ρHg g h
D. P = ρ Hg g h + P 0
E. None of the above
- Which of the following statements is false about Bernoulli's equation (BE)?
A. BE is a consequence of conservation of energy
B. BE is applicable for any flow speed, v C. BE is applicable in a space ship
D. BE is applicable even if the net work done by the fluid is zero
E. BE is applicable even when viscosity of fluid is large
