Question

A ball is dropped from the top of a tower of unknown height. If the ball travels $35m$ in the last second of its journey, find the height of the tower. ​ $(Takeg=10m{s}^{-2})$

• A. $80m$
• B. $40m$
• C. $60m$
• D. $70m$

Answer 1

The correct option is A $80m$

Equation distance of freely falling body in total t seconds is given by:
$s_1=\frac{1}{2}\times g\times t^2$

For $t-1$ second it would be:
$s_2=\frac{1}{2}\times g\times (t-1{)}^2$
Distance covered in last second is nothing but $s_1–s_2$.​
Height of tower is $s_1$, it can be calculated after obtaining t.​ ​