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**1. Homework Statement**

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

**2. Homework Equations**

N=ma

m= w/g

**3. The Attempt at a Solution**

I started out by trying to draw a picture. So I got:

F3(total box) = F1 + F2

F1= (m)(a) --> a= 0 since V is constant? So F1= 0

F2= 0.2 (100) = 20

F3= 0+20 = 20

W(total box) = (F)(d)= (20)(100) = 2000 lb(ft) or 2.57 Btu

That's the work for the box I think? But then how to add in the force of the man's weight? Thank you so much in advance.

I started out by trying to draw a picture. So I got:

F3(total box) = F1 + F2

F1= (m)(a) --> a= 0 since V is constant? So F1= 0

F2= 0.2 (100) = 20

F3= 0+20 = 20

W(total box) = (F)(d)= (20)(100) = 2000 lb(ft) or 2.57 Btu

That's the work for the box I think? But then how to add in the force of the man's weight? Thank you so much in advance.