10. A 3 kg block moves up a 40° incline with constant speed under the action of a 26N force acting up and parallel to the incline. What magnitude force must act up and parallel to the incline for the block to move down the incline at constant velocity?

Answer 1

Normal force = m g cos 40
During trip up:
Friction force down slope = mu m g cos 40
Gravity force down slope = m g sin 40
26 - m g sin 40 - mu m g cos 40 = 0
solve that for mu, friction coef

During trip down
friction force now up slope
F - m g sin 40 + mu m g cos 40 = 0
solve that for F

Answer 2

Damon what is the value for mu when there wasn't anything about it stated in the question.

Answer 3

You need to read thoroughly from beginning to ending of what he wrote