Question

A frictionless disc of mass 0.50 kg is moving in a straight line across an air table at a speed of 2.4 m/s when it bumps into an elastic band stretched between two fixed posts. If the elastic band exerts an average opposing force of 1.4 N on the disc for 1.5 s, what will be the final velocity of the disc?

Answer 1

Find the acceleration experienced by the disc:

$$a=F/m.$$

Find the final velocity of the disc:

$$v=v_0-at=v_0-Ft/m=-1.8\text{ m/s}.$$

The negative velocity means that the disc will move in the opposite direction.