Question

A person pushes horizontally on a heavy box and slides it across the level floor at constant velocity. The person pushes with a 60.0 N force for the first 16.4 m at which time he begins to tire. The force he exerts then starts to decrease linearly from 60.0 N to 0.00 N across the remaining 6.88 m. How much total work did the person do on the box

Answer 1

Over the first 16.4 m, the person performs

W = (60.0 N) (16.4 m) = 984 J

of work.

Over the remaining 6.88 m, they perform a varying amount of work according to

F(x) ≈ 60.0 N + (-8.72 N/m) x

where x is in meters. (-8.72 is the slope of the line segment connecting the points (0, 60.0) and (6.88, 0).) The work done over this interval can be obtained by integrating F(x) over the interval [0, 6.88 m] :

W = ∫₀⁶˙⁸⁸ F(x) dx ≈ 206.4 J

(Alternatively, you can plot F(x) and see that it's a triangle with base 6.88 m and height 60.0 N, so the work done is the same, 1/2 (6.88 m) (60.0 N) = 206.4 J.)

So the total work performed by the person on the box is

984 J + 206.4 J = 1190.4 J ≈ 1190 J