Q 11-02-010NEETNEET 2020Top questionEasy
A ball is thrown vertically downward with a velocity of $20$ m/s from the top of a tower. It hits the ground after some time with a velocity of $80$ m/s. The height of the tower is : ($g = 10\ \text{m/s}^2$)
Answer: (D) $300$ m
Concept. $v^2 = u^2 + 2gh$ for motion downwards under gravity.
Step 1. Substitute.
$$6400 = 400 + 20h \;\Rightarrow\; h = 300\ \text{m}$$
Answer. $300$ m (Option D).
Solution by Sreeraj P, M.Sc Physics