A man wants to move a 53.0 kg box across a level floor, for which the coefficient of kinetic friction is 0.55. After he has started the box moving, what strength force he will he need to push with to keep it moving at a constant speed?

Question

anonymous · Answer

To keep the box moving at constant speed, the applied force will be equal in magnitude to the friction force. Can you determine the friction force?

anonymous · Answer

Would you do it by taking mg?

anonymous · Answer

That will give you the gravitational force, or weight. Best to look at a free body diagram:|dw:1447114698575:dw|

anonymous · Answer

So, calculate $F_g$ as you mentioned above. The normal force, $F_n$, has the same magnitude. Then, calculate the friction force, $F_f$ using$$F_f = \mu F_n$$Finally the applied force, $F_a$ must have the same magnitude as the friction force for the object to move with constant velocity.

anonymous · Answer

@ospreytriple but what would you put for the mu?

anonymous · Answer

Because for Fgrav = 519.93 so Fnorm would be the same.

anonymous · Answer

Good. $\mu$ is the coefficient of kinetic friction which is given in the problem.

anonymous · Answer

So it's the .55N?