Question

A ball of mass 22 g moves to the left at a speed of 35 m / s. How much work needs to be done on the ball to start moving to the right at a speed of 35 m / s. When considering ignore any energy losses.

Answer 1

The work required to make it move in the opposite direction at the same is speed can be calculated from law-energy theorem. First, we need to stop the object from 35 to 0:

$$W_1=\frac12mv^2.$$

Next, we need to accelerate the object from 0 to 35 m/s:

$$W_2=\frac12mv^2.\\\space\\ W=W_1+W_2=mv^2=26.95\text{ J}.$$