Question

A ball is released from a height of 20N. Calculate

a. The time it takes to fall

b. The velocity to which it hits the ground

Answer 1

(a) We can find the time it takes to fall as follows:

$$h=\dfrac{1}{2}gt^2,$$ $$t=\sqrt{\dfrac{2h}{g}}=\sqrt{\dfrac{2\times20\ m}{9.8\ \dfrac{m}{s^2}}}=2.02\ s.$$

(b) We can find the velocity to which it hits the ground from the kinematic equation:

$$v=v_0+gt=-9.8\ \dfrac{m}{s^2}\times2.02\ s=-19.8\ \dfrac{m}{s^2}.$$

The sign minus means that the velocity of the ball directed downward.