Question

A 200-foot cable weighing 800 pounds is hanging from a winch 200 feet above ground level.

(a) How much per foot does this cable weigh? if a piece of this cable is A.x long, what is the weigh of this piece?
(b) Find the work (in ft-lb) done in winding up the cable when there is a 400- pound load attached to the end of the cable.

Answer 1

4 pd / ft

140000 ft/pd

Explanation:

Total Weight of cable = 800 pounds

Length of cable = 200 feets

Weight per foot = Total weight / length = 800 / 200 = 4 pounds per foot

Weight of piece will be :

Weight of cable - weight per foot * x

800 - 4x

Workdone with 300 pound load attached :

∫f(x)

f(x) = (800+300 - 4x) = 1100 - 4x

∫1100 - 4xdx at 200 to 0

Integrating the above

1100x - 4/2x² at x = 200 to 0

1100x - 2x²

1100(200) - 2(200²) - 1100(0) + 2(0^²))

(220000-80000) - 0 + 0

140000 ft/pd