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.
150 ft-lb
300 ft-lb
2,400 ft-lb
1,200 ft-lb
600 ft-lb
____ 6. Neglecting air resistance and the weight of the propellant, determine the work done in
propelling a six-ton satellite to a height of 200 miles above earth. Assume that Earth has a radius of
4000 miles.
ft-lb
ft-lb
ft-lb
ft-lb
ft-lb
____ 7. Neglecting air resistance and the weight of the propellant, determine the work done in
propelling a 12-ton satellite to a height of 100 miles above Earth. Assume that the Earth has a
radius of 4000 miles.
1,756.10 mi-ton
1,170.73 mi-ton
702.44 mi-ton
936.59 mi-ton
2,575.61 mi-ton
____ 8. A lunar module weighs 16 tons on the surface of Earth. How much work is done in
propelling the module from the surface of the moon to a height of 50 miles? Consider the radius of
the moon to be 1100 miles and its force of gravity to be one-sixth that of Earth.
ft-lb
ft-lb
ft-lb
ft-lb
ft-lb