Question

Why is tension of a string attached between a mass and an elevator ceiling greater when the elevator is moving upwards than when it is at rest?

Answer 1

When the elevator is at rest, the cable is providing the force equal and opposite to gravity to keep the elevator at rest.

However, when the elevator is accelerating upwards, the force on the cable must both be the gravitational force and the additional force required to have a net upward force for the acceleration.

Notice that if the elevator is traveling upwards at a constant speed, the net force on the elevator is zero and in that case the tension in the cable is just equal in magnitude to the gravitational force.

Answer 2

ohhhhh ok thanks!