Problem 9.

Part a of the drawing shows a block suspended from the pulley; the tension in the rope is 80 N. Part b shows the same block being pulled up at a constant velocity. What is the tension in the rope in part b ?

Solution:

In part (a) the equilibrium condition can be written as:

In part (b) we have the motion with constant velocity. It means that the acceleration is 0 and the net force is 0, which can be written as

From these two equations we can find