A tennis ball of mass m = 0.075 kg is thrown straight up with an initial speed v0 = 12 m/s. Let the gravitational potential energy be zero at the initial height of the tennis ball.

Question

m = 0.075 kg	v0 = 12 m/s

What is the maximum height, h in meters, the ball reaches? 

What is the work done by gravity, W_g in Joules, during the ball's flight to its maximum height? 

Answer 1

Since gravity is constant, you can use a uniform acceleration equation:

v_f² = v₀² + 2ad, where v is the velocity, a is the acceleration due to gravity, and d is the displacement. You are given v_o, you should know the gravitation acceleration, and with some careful thinking, you can logically conclude what v_f must be when the ball reaches its maximum height. So then you simply need to solve for the displacement.

Work is simply the change in kinetic energy plus the change in potential energy. If there is no potential energy at the ball's initial launch, then it's energy is made up entirely of kinetic energy. Once the ball reaches it's peak, it has no kinetic energy left. Therefore, the change in energy is simply how much kinetic energy the ball had at the very beginning.

Use the formula to for calculating kinetic energy to figure out how much work gravity did.