Download 2008 Mechanical Energy Unit Test

Mechanical Energy
36
Part I - Multiple Choice
1. A force of 75 N is applied at a 30.° angle to the horizontal in order to move a 15 kg object 12
m along a surface. A 10. N frictional force acts as in the diagram below.
The work done is
A. 900 J
B. 780 J
C. 650 J
D. 450 J
2. A 6.00 kg mass is released vertically from rest at a height of 80.0 m. If air resistance is
neglected, the kinetic energy of the mass when it has fallen 60.0 m is
A. 4 .70  10 J
B. 3.53  10 J
3
C. 1.18  10 J
3
D. 1.20  10 J
2
Use the following information and diagram to answer questions 3 - 6.
A 0.25 kg ball is rolling along a frictionless track, as shown in the diagram below.
3. The work required to raise the ball from ground level to point B is
A. 0 J
B. 2.5 J
C. 20. J
D. 78 J
4. The ratio of the ball’s potential energy at point B to its potential energy at point A is
A. 5 : 8
B. 8 : 5
C. 25 : 64
D. 64 : 25
5. If the ball were released from rest at point B, what speed would it have at point A?
A. 7.7 m/s
B. 9.9 m/s
C. 13 m/s
D. 98 m/s
6. In inelastic interactions heat is produced but
A. total energy remains the same.
B. the mechanical energy remains the same.
C. kinetic energy remains the same.
D. potential energy increases.
7. Work can never be done when the direction of the applied force acting on a given object is
A. parallel to the displacement of the object.
B. in the same direction as the motion of the object
C. perpendicular to the displacement of the object.
D. in the opposite direction of the motion of the object.
8. During elastic collisions,
A. kinetic energy is conserved.
B. potential energy is conserved.
C. thermal energy is produced.
D. mechanical energy is conserved.
9. If you triple the velocity of an object you would change its kinetic energy by a factor of
A. 9
B. 6
C. 3
D. 1/3
Part II: Short Answer. Fully answer each question for full marks!
1. Differentiate between potential energy and kinetic energy. Explain how the two are related in
the total mechanical energy of a system. (3 marks)
2. A stone thrown vertically upward with an initial velocity of 50.0 m/s will reach what final
height? (3 marks)
3. Batman and Robin were in competition with each other to see who could do more work and
therefore who was stronger. They decided to carry 1000 pounds of bricks 1 mile. Batman
quickly loaded himself up and took of with superhuman speed and strength; Robin however took
his time to move the same load. After Batman had waited for 30 minutes at the finish line Robin
pulled up and began unloading his bricks.
“Aha!” said Batman, “I am clearly stronger than you because you didn’t do the work that I did!”
“No,” replied Robin, “we clearly have the same strength because our work is equal.”
Who is correct and why? Who is more powerful and why? (2 marks)
4. A stationary 0.325 kg steel ball begins rolling from rest form a height, h, down a frictionless
track. It completes a loop-the-loop of radius 1.20 m with a speed of 6.00m/s at the top of the
loop. Using the diagram below, from what height, h, was the ball released? (4 marks)
5. A force of 450 N is applied to a box at an angle of 60.° from the vertical as shown in the
diagram. The mass of the box is 7.5 kg and it moves along a frictionless, horizontal surface.
The work done on the box is 5 900J. How far did the box move horizontally? (4 marks)
6.A 6.00kg mass is released vertically from rest at a height of 80.0 m. If air resistance is
neglected, what is the kinetic energy of the mass when it has fallen 60.0 m? (4 marks)
7. A 1.75 kg coconut falls out of a tree 13.5 m tall and hits a 1.67 m tall bystander on the top of
the head. It bounces up 0.24 m before continuing to fall the rest of the way to the ground.
a) How much potential energy does it have before it falls? (2 marks)
b) How fast is the coconut going the instant before it hits the unfortunate bystander? (3 marks)
c) What is the total amount of work done on the coconut? (2 marks)