ِAn Overhead Garage Door Has Two Springs, One on Each

Multiple Choice

ِAn overhead garage door has two springs, one on each side of the door. A force of 12 pounds is required to stretch each spring 1 foot. Because of the pulley system, the springs stretch only One-half the distance the door travels. The door moves a total of 10 feet and springs are at their Natural length when the door is open. Find the work done by pair of strings.

A) 150 ft-lb
B) 300 ft-lb
C) 2,400 ft-lb
D) 1,200 ft-lb
E) 600 ft-lb