A man weighing 180 lbf pushes a block weighing 100 lbf along a horizontal plane. The dynamic

Question:

A man weighing 180 lbf pushes a block weighing 100 lbf along a horizontal plane. The dynamic coefficient of friction between the block and plane is 0.2. Assuming that the block is moving at constant speed, calculate the work required to move the block a distance of 100 ft considering
(a) The man and
(b) The block as the system. Express your answers in both lbf·ft and Btu.