How much work is required to lower a 120-pound weight from the top of a 3-foot table to the floor?

How much work is required to lower a 120-pound weight from the top of a 3-foot table to the floor?

• A. 120 foot-pounds
• B. 240 foot-pounds
• C. 360 foot-pounds
• D. 480 foot-pounds

Answer: (C)

Work is the product of force and the distance the force acts through. The weight provides a downward force of 120 pounds, and the weight moves downward 3 feet, in the same direction as that force. So the work associated with the drop is 120 pounds × 3 feet = 360 foot-pounds. If you lower it slowly, your muscles would do negative work equal in magnitude to that amount (you absorb energy while gravity does the positive 360 ft-lb of work). The key point is the energy transferred due to the height change, which is 360 foot-pounds.

Work is the product of force and the distance the force acts through. The weight provides a downward force of 120 pounds, and the weight moves downward 3 feet, in the same direction as that force. So the work associated with the drop is 120 pounds × 3 feet = 360 foot-pounds.

If you lower it slowly, your muscles would do negative work equal in magnitude to that amount (you absorb energy while gravity does the positive 360 ft-lb of work). The key point is the energy transferred due to the height change, which is 360 foot-pounds.