1017-311 (Dr. O’Dea) University Physics I Exam #3
Practice Exam
Name: ______
Exam Score: ______
READ the following instructions:
1. The exam is closed book and closed notes.
2. Calculators and the equations provided below are allowed.
3. For numerical problems: Show all of your work.
Generally, you should show a minimum of four steps.
Diagram, if appropriate.
What general equation are you "plugging into"?
What are your substitutions? Be certain to include UNITS with numbers.
What is your final answer? Place a box around your final answer.
Near earth g = 9.8 m/s2
1. A spacecraft is separated into two parts by detonating the explosive bolts that hold them together. The masses of the parts are 1200 kg and 1800 kg. The magnitude of the impulse on each part from the bolts is 400 N-s. With what relative speed do the two parts separate because of the detonation?
2. A railroad flatcar of weight W can roll without friction along a straight horizontal track. Initially, a man of weight w is standing on the car, which is moving to the right with speed v1 (see Figure). What is the change in velocity of the car if the man runs to the left (in the Figure) so that his speed relative to the car is vrel?
3. Two skaters, one with mass 80 kg and one with mass 45 kg, stand on an ice rink holding a pole of length 10m and negligible mass. Starting from the ends of the pole, the skaters pull themselves along the pole until they meet. How far does the 54 kg skater move?
4. A 5.0 kg block moves in a straight line on a horizontal frictionless surface under the influence of a force that varies with position as shown in the Figure. How much work is done by the force as the block moves from the origin to x = 8.0 m?
5. In the Figure a small block of mass m can slide along the frictionless loop-the-loop. The block is released from rest at point P, at height h=5R above the bottom of the loop. How much work does the gravitational force do on the block as the block travels from point P to (a) point Q, and (b) the top of the loop? If the gravitational potential energy of the block-Earth system is taken to be zero at the bottom of the loop, what is the potential energy when the block is (c) at point P, (d) at point Q, and (e) at the top of the loop? (f) If, instead of being released, the block is given some initial speed downward along the track, do the answers to (a) through (e) increase, decrease, or remain the same?
1. A 1.0-kg ball moving at 2.0m/s perpendicular to a wall rebounds from the wall at 1.5m/s. The change in the momentum of the ball is:
A. zero
B. 0.5N·s away from wall
C. 0.5N·s toward wall
D. 3.5N·s away from wall
E. 3.5N·s toward wall
2. A 5-kg object can move along the x axis. It is subjected to a force in the positive x direction; a graph of Fx as a function of time t is shown below. Over the time the force is applied the change in the velocity of the object is:
A. 0.8m/s
B. 1.1m/s
C. 1.6m/s
D. 2.3m/s
E. 4.0m/s
3. A 1000-kg space probe is motionless in space. To start moving, its main engine is fired for 5s during which time it ejects exhaust gases at 5000m/s. At the end of this process it is moving at 20m/s. The approximate mass of the ejected gas is:
A. 0.8kg
B. 4kg
C. 5kg
D. 20kg
E. 25kg
4. The x and y coordinates of the center of mass of the three-particle system shown below are:
A. 0,0
B. 1.3m, 1.7m
C. 1.4m, 1.9m
D. 1.9m, 2.5m
E. 1.4m, 2.5m
5. Block A, with a mass of 4kg, is moving with a speed of 2.0m/s while block B, with a mass of 8kg, is moving in the opposite direction with a speed of 3m/s. The center of mass of the two block-system is moving with a velocity of:
A. 1.3m/s in the same direction as A
B. 1.3m/s in the same direction as B
C. 2.7m/s in the same direction as A
D. 1.0m/s in the same direction as B
E. 5.0m/s in the same direction as A
6. A 640-N hunter gets a rope around a 3200-N polar bear. They are stationary, 20m apart, on frictionless level ice. When the hunter pulls the polar bear to him, the polar bear will move:
A. 1.0m
B. 3.3m
C. 10m
D. 12m
E. 17m
7. Let and . Then
A.
B.
C. 23m2
D. 17m2
E. none of these
8. A crate moves 10m to the right on a horizontal surface as a woman pulls on it with a 10-N force. Rank the situations shown below according to the work done by her force, least to greatest.
A. 1, 2, 3
B. 2, 1, 3
C. 2, 3, 1
D. 1, 3, 2
E. 3, 2, 1
9. An object moves in a circle at constant speed. The work done by the centripetal force is zero because:
A. the displacement for each revolution is zero
B. the average force for each revolution is zero
C. there is no friction
D. the magnitude of the acceleration is zero
E. the centripetal force is perpendicular to the velocity
10. Camping equipment weighing 6000N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. How much work is done by the campers in pulling the equipment 1000m if its speed is increasing at the constant rate of 0.20m/s2?
A. –1.2´106J
B. 1.8´105J
C. 3.0´105J
D. 4.2´105J
E. 1.2´106J