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 moves at a constant speed, how much work is required to move the block 100 ft considering the (a) the block and (b) the man as the system.

The first thing you should know is that the work is defined as:

W = F * d

Where

F = force

d = displacement

We have then

(a) the block

F = (0.2) * (100) = 20

d = 100

W = (20) * (100) = 2000 ft. lbf

(b) the man as the system.

F = (0.2) * (100 + 180) = 56

d = 100

W = (56) * (100) = 5600 ft. lbf

answer:

(a) 2000 ft. lbf

(b) 5600 ft. lbf