Question Detail
Question
A 120 N concrete block rests on a 30° inclined plane with μk = 0.5. If a push P parallel to the plane and directed up the plane is applied to keep the block in equilibrium (moving at constant speed), what must P balance?
Correct Answer
Option C is the correct answer.
Detailed Explanation
For equilibrium (constant velocity) with a push up the plane, both the component of weight down the plane (60 N) and the kinetic friction force down the plane (which opposes motion) must be overcome. The push P must equal the sum of these two forces.
Hint
If the block is being pushed up, friction acts down the plane, opposing that motion. So both gravity and friction are acting in the downward direction along the plane.