Question

A tennis ball is thrown upwards with sufficient speed to reach a height of 12 m.

(i) What is the kinetic energy of the tennis ball at a height of 12 m?

(ii) Calculate the speed of the tennis ball when it reaches a height of 6 m.

Answer 1

(i) What is the kinetic energy of the tennis ball at a height of 12 m?

Answer: zero

(ii) Calculate the speed of the tennis ball when it reaches a height of 6 m.

$$\frac{mv^2}{2}+mgh_2=mgh_1$$

$$v=\sqrt{2g(h_1-h_2)}$$

$$v=\sqrt{2*9.8(12-6)}=11\:\rm m/s$$