Physics 40 Exam 2 Practice
Name: __________________________________
Ignore air resistance and friction unless told otherwise.
Conceptual Questions. (2 pts) Circle the BEST answer.
1. The area under the graph to the right gives:
a. energy
b. work
c. impulse
d. force
2. The area under the graph to the left gives:
a. energy
b. work
c. impulse
d. force
3. As the car goes around the loop, where is the normal force the greatest?
a. top
b. bottom
c. side
d. same all around
4. When a ball rises vertically to a height h and returns to its original point of projection, the work done by the
gravitational force is
a. 0.
b. −mgh .
c. +mgh.
d. –2mgh.
e. +2mgh.
5. Is momentum conservation violated in this collision event?
a. yes
b. no
6. Which requires the most amount of work on the brakes of a car?
a. Slowing down from 100 km/h to 70 km/h
b. Slowing down from 70 km/h to a stop.
7. The value of the momentum of a system is the same at a later time as at an earlier time if there are no
a.
b.
c.
d.
e.
collisions between particles within the system.
inelastic collisions between particles within the system.
changes of momentum of individual particles within the system.
internal forces acting between particles within the system.
external forces acting on particles of the system.
Short Problems (10 points each). Box your answer. Show your work for ANY credit.
1. Two blocks in contact with each other are pushed to the right across a
rough horizontal surface by the two forces shown. If the coefficient of kinetic
friction between each of the blocks and the surface is 0.30, determine the
magnitude of the force exerted on the 2.0-kg block by the 3.0-kg block.
a.
b.
c.
d.
e.
30N
2.0 kg
3.0 kg
15 N
25 N
11 N
22 N
33 N
2. M = 6.0 kg, what is the tension in string 1?
30˚
30
1
a.
b.
c.
d.
e.
39 N
34 N
29 N
44 N
51 N
60
60˚
2
M
3. A 2.0-kg block sliding on a rough horizontal surface ( μ = 0.45) is attached to one end of a horizontal spring (k = 250
N/m) which has its other end fixed. The block passes through the equilibrium position with a speed of 2.6 m/s and then
compresses the spring a distance x from equilibrium Find the distance x that that the spring is compressed. Sketch the
situation and draw a vector diagram of the block.
a.
b.
c.
d.
e.
0.32
0.45
0.58
0.19
0.26
10N
4. A 4.0-kg mass has a velocity of 4.0 m/s, east when it explodes into two 2.0-kg masses. After the explosion one
of the masses has a velocity of 3.0 m/s at an angle of 60° north of east. What is the magnitude of the velocity of
the other mass after the explosion?
a.
b.
c.
d.
7.9 m/s
8.9 m/s
7.0 m/s
6.1 m/s
e.
6.7 m/s
5. A 0.60-kg object is suspended from the ceiling at the end of a 2.0-m string. When pulled to the side and released, it has a
speed of 4.0 m/s at the lowest point of its path. What is the tension in the string when the object reaches the maximum height
as it swings up? Sketch and label the situation.
a.
b.
c.
d.
e.
61°
54°
69°
77°
47°
6. A 2.0-kg particle has an initial velocity of (5i – 4j) m/s. Some time later, its velocity is (7i + 3j) m/s.
How much work was done by the resultant force during this time interval, assuming no energy is lost
in the process?
a.
b.
c.
d.
e.
17 J
49 J
19 J
53 J
27 J
Long Problems
1. In the figure shown, the coefficient of kinetic friction between the block
and the incline is 0.29. Disregard any pulley mass or friction in the pulley.
Draw free body diagrams of both masses. Find the acceleration of the
masses and the tension in the string. M = 1.00 kg. The angle is 30 degrees.
2M
30˚
30
M
2. A roller-coaster car is released from rest as shown and then moves
freely with negligible friction. The roller coaster has a circular loop of
radius R in a vertical plane. The roller-coaster falls from rest from a
height 3R above the bottom of the loop.
1. What is the speed at the top of the loop? Draw a free body diagram
of the car at the top of the loop. Will the car have enough speed to
make it around the loop? Justify your answer.
2. Find the normal force at the top of the loop and express it as a
factor of g, the acceleration due to gravity.
3. Find the speed and normal force at the bottom of the loop. Are these safe values?