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Unit 5, Quiz #2

KE = (1/2) m v2
P = W/t
W = F d costheta
Fnet = m a
PE = m g h
Fgrav = m g

1. As a rock free-falls from a cliff, its total mechanical energy is equal to

a. its potential energy minus its kinetic energy.

b. its kinetic energy minus its potential energy.

c. the product of its kinetic and potential energies.

d. the sum of its potential and kinetic energies.

Use the diagram to answer questions #2 - #4. Neglect the effect of friction and air resistance.

2. As the ball rolls from point A to point D across the frictionless surface, the sum or total of its potential and kinetic energies

a. decreases, only.

b. decreases and then increases.

c. increases and then decreases.

d. remains the same.

3. The ball will have a minimum gravitational potential energy at point

a. A

b. B.

c. C.

d. D.


4. The ball's kinetic energy at point B is less than its kinetic energy at point . .

a. A only.

b. A, D, and E.

c. C only

d. C, D and E.

e. D and E

5. Construct a work-energy bar chart for the following physical description.

A skier starts from rest on top of hill A and skis into the valley and back up onto hill B. See diagram at the right. The skier utilizes her poles, applying a force to propel herself across the snow. The initial state is on top of hill A and the final state is on top of hill B. Ignore frictional forces.

6. An 800-kg car moving at 25.0 m/s runs out of gas just prior to ascending (climbing) a hill. Supposing that -40000 J of work are done upon the car by air resistance (and other external forces), determine a) its potential energy when it reaches its highest point along the hill before momentarily stopping, and b) the height to which the car will coast up the hill before stopping. PSAYW




7. Near the end of a roller coaster ride , a braking system applies a large force to bring the 5000-kg train of cars from a speed of approximately 20 m/s to a speed of 5 m/s over a distance of 20 meters (see diagram). Determine the force. PSYW




Allison Wonderland (60-kg) is swinging in a chair. She starts from rest at a height of 3.2-m above the ground (position A). At position B, she is 1.0 m above the ground. At position C (1.9 m above the ground), she projects from the seat and travels as a projectile along the path shown. At point F, she is a mere picometer above the ground. Assume negligible air resistance throughout the motion.

Use this scenario to answer questions #8-12.

8. Carefully construct energy-bar charts for this motion at the five indicated positions (omit E).

9. Determine the total mechanical energy of Alice. PSYW



10. Determine the Alice's speed at position B. PSYW



11. Determine the Alice's speed at position F. PSYW



12. If an 80-kg swinger did the same motion, would the landing speed (at position F) be greater than, less than, or equal to the final speed of the 60-kg swinger? Explain clearly and logically.


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Last updated on 12/9/04.