Question

A ball is dropped from the top of a tower of an unknown height. If the ball travels 35 m in the last second of its journey, find the height of the tower. (Take g = 10 $m/s^2$)

• A. 80 m
• B. 60 m
• C. 90 m
• D. 120 m

Answer 1

The correct option is A 80 m

Newton’s 3rd equation of motion,
S = $\frac{1}{2}g{t}^2$ [u = 0, dropped]​

S - 35 = $\frac{1}{2}g(t-1{)}^2$​

On solving, we get, ​
t = 4 s​

On putting t = 4 s in the 3rd equation of motion, we get, ​
S = 80 m​