A man weighs 171lbf pushes a block that weighs 81lbf along a

A man weighs 171lbf pushes a block that weighs 81lbf along a horizontal plane. The dynamic coffecient of friction betweeen the block and the plane is .22. Assuming that the blockis moving at a constant speed, caculate the work required to move the block a distance of 144ft considering (a) the man and (b) the block as the system. Express your answer in both lbf-ft and Btu.

A) W=            lbf-ft       W=          Btu

B) W=            lbf-ft       W=          Btu

Solution

A) work done in lbf = 171 x 144 = 24624 , I feet = .001285 btu, = 31.64356 btu

B) work done on block in lbf = 1.22 x 81 x 144 =14230,

Total work on system = 14230+24624= 38854 lbf ft

= 49.93 btu