A 45-kg box is being pushed a distance of 6.6 m across the floor by a force P wi
ID: 1313499 • Letter: A
Question
A 45-kg box is being pushed a distance of 6.6 m across the floor by a force P with arrow whose magnitude is 169 N. The force P with arrow is parallel to the displacement of the box. The coefficient of kinetic friction is 0.23. Determine the work done on the box by each of the four forces that act on the box. Be sure to include the proper plus or minus sign for the work done by each force. (The floor is level and horizontal. Forces that act on the box: pushing force P, frictional force f, normal force N, and weight mg.)
WP = J
Wf = J
WN = J
Wmg = J
Explanation / Answer
Work done by the applied force is simply force * distance =169*6.6=1115.4 j
Work done by friction is the same idea. Solve for the force of friction and multiply it by distance to find work done by friction. =mu*mg*distance=0.23*45*9.8*6.6=669.438 j
The other two didn't do work because the box didn't move up or down. You can also think of it this way. W = Fdcos[theta]
cos90 = 0
Because the normal force and the force of gravity are perpendicular to the surface, they don't do work.
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