111,
Exam A
Physics 3A
Part I. Put the answers to these 12 questions on your SCANTRON sheet. Your answer should be CLOSEST TO THE GIVEN
1) An 1800-kg car stopped at a traffic light is struck from the rear by a 900 -kg car and the two become entangled. If the
smaller car was moving at 20m/s before collision, what is the speed of the entangled mass after the collision?
a) 6.67 m/s
b) 0 m/s
c) 10.23 m/s
d) 0.67 m/s
e) 300 m/s
2) A body of mass 2.0-kg makes an elastic collision with another body at rest and continues to move in the original
direction but with one fourth (1/4) of its original speed. What is the mass of the other body?
a) 4.2-kg
b) 1.2-kg
c) 3.7-kg
d) 0.6-kg
e) 29-kg
3) Two titanium spheres approach each other head on with the same speed and collide elastically. After the collision, one
of the spheres, whose mass is 300-g, remains at rest. What is the mass of the other sphere?
a) 0.6-kg
b) 0.1-kg
c) 1.5-kg
d) 2.9-kg
e) 10.2-kg
4)
What is the magnitude of the angular velocity of a spaceship taking a circular turn of radius 3220 km at a speed of
29000 km/h?
a) 200 rad/h
b) 0.1 rad/h
c) 49 rad/h
d) 9 rad/h
e) 15 rad/h
=
3
t
5) The angular position of a point on the rim of a rotating wheel is given by 4.0 t .0 t 2 +3 , where
is in
radians and t in seconds. What is the average angular acceleration for the time interval that begins at t = 2s and ends at
t = 4s?
a) 200 rad/s2
b) 12 rad/s2
c) 0.1 rad/s2
d) 5 rad/s2
e) 34 rad/s2
6) A disk, initially rotating at 120 rad/s, is slowed down wit a constant angular acceleration of magnitude 4.0 rad/s . How
2
much time does the disk take to stop?
a) 0.1 s
b) 130 s
c) 90 s
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Physics 111,
Exam 3A
d) 30 s
e) 0.3 s
A
7) A flywheel with diameter of 1.2 m is rotating at an angular speed of 200 rad/min. What constant angular acceleration
will increase the wheels angular speed to 1000 rad/min in 60 s?
a) 800 rad/min2
b) 92.5 rad/min2
c) 0.8 rad/min2
d) 200 rad/min2
e) 5 rad/min2
8) The body in figure 1 is pivoted at O, and two forces act on it as shown. If r =1.30 m, r =2.15 m, F =4.20 N, F =4.90 N,
1
2
1
2
1 = 75 and 2 60 = . What is the net torque about the pivot?
a) 7.29 Nm
b) -3.85 Nm
c) -7.29 Nm
d) 3.85 Nm
e) 342.5 Nm
0
0
9) The rigid body shown in figure 2 consists of three particles connected by massless rods.
M=0.4 -kg, a=30 cm and b=50cm. What is the rotational inertia of the rigid body about
an axis perpendicular to its plane through point P?
a) 13.6-kg m2
b) 5.93-kg m2
c) 125-kg m2
d) 0.75-kg m2
e) 0.136-kg m2
10) A small ball with mass 1.3-kg is mounted on one end of a thin, uniform rod 0.78 m long and of mass 7.8-kg. The
system rotates in a horizontal circle about the other end of a rod. What is the rotational inertia about the axis of
rotation?
a) 9.42-kg m2
b) 7.32-kg m2
c) 2.37-kg m2
d) 0.92-kg m2
e) 50.21-kg m2
11) What is the rotational inertia of a wheel that has a kinetic energy of 24400 J when rotating at 602 rev/min?
a) 0.92-kg m2
b) 12.30-kg m2
c) 112.3-kg m2
d) 18.9-kg m2
e) 121.20-kg m2
12) If a 32.0 N m torque on a wheel causes angular acceleration of 25 rad/s , what is the wheels rotational inertia?
2
a) 5.64-kg m2
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Physics 111,
Exam 3A
b) 1.28-kg m2
c) 3.40-kg m2
d) 200-kg m2
e) 22.39-kg m2
A
3
A
Physics 111,
Exam 3A
Part II. Workout Problems. To get partial credit you must show your work.
1) (2 points) A bullet of mass 10 g strikes a ballistic pendulum of mass 2-kg. The center of mass of the pendulum rises a
vertical distance of 12 cm. Assuming that the bullet remains embedded in the pendulum, calculate the bullets initial speed.
2) (3 points) In Figure 3, one block has mass M=0.5-kg, the other has mass m=0.46-kg, and the pulley, which is mounted in
horizontal frictionless bearings has a radius of 0.05 m. When released from rest, the more massive block falls 0.75 m in 5 s
(without the cord slipping on the pulley).
What is:
a) The magnitude of the blocks acceleration?
b) The tensions T
1 and T2?
c) Magnitude of pulleys angular acceleration?
d) The rotational inertia?
T1
T2
m
M
4
Physics 111,
Exam 3A
A
1a,2b,3b,4d,5b,6d,7a,8b,9e,10c,11b,12b
workout 1 V=308.25 m/s
workout 2 a=0.06 m/s; T1= 4.57 N; T2= 4.87 N; =1.2 rad/s2;
I=0.25 -kg m2
5