What is the frictional force between a box and the floor it is being pulled across if, the kinetic coefficient of friction is 0.27 and the box weighs 38 N?
A 140.7 N
B 100.6 N
C. 37.7 N
D. 10.3 N

If the pulling is done parallel to the floor with constant velocity, then the box is in equilibrium. In particular, the weight and normal force cancel, so that

n = 38 N

The friction force is proportional to the normal force by a factor of 0.27, so that

f = 0.27 (38 N) ≈ 10.3 N

and so the answer is D.

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