Question

A pebble is dropped from the top of a 25-m tall building. How long will it take before the

pebble hits the ground?

Answer 1

$$h=\dfrac{1}{2}gt^2,$$ $$t=\sqrt{\dfrac{2h}{g}}=\sqrt{\dfrac{2\times25\ m}{9.8\ \dfrac{m}{s^2}}}=2.26\ s.$$