Question

If a ball is dropped from rest, it will fall 20m during the first two seconds. How far will it fall during the third and fourth seconds?

• A. $20m$
• B. $35m$
• C. $40m$
• D. $50m$
• E. $60m$

Answer 1

The correct option is B $35m$

Given,

Displacement $20m$ in first $2\sec .$

Apply kinematic equation

$s=ut+\frac{1}{2}a{t}^2$

$20=0+\frac{1}{2}a\times 2^2$

$a=10m{s}^{-2}$

Displacement in $3^{th}to{4}^{th}\sec$

$S_4-S_3=\frac{1}{2}a(t_2^2-t_1^2)=\frac{1}{2}\times 10(4^2-3^2)$

$S_4-S_3=35m$

Hence, ball dropped $35m$ in third to fourth second.