Question

Two balls are dropped to the ground from different heights. One ball is dropped $2s$ after the other but both of them strike the ground simultaneously $5s$ after the first is dropped. The difference in the heights, when they are dropped is ($g=10m/s^2$)

• A. 80 m
• B. 45 m
• C. 95 m
• D. 100 m

Answer 1

The correct option is A 80 m

Ball B is dropped first. Then, ball A is dropped after 2 s.
$h_B=\frac{1}{2}g{t}^2=\frac{1}{2}g(5{)}^2=12.5g=\frac{25g}{2}$ ....... (1)

$h_A=\frac{1}{2}g{t}^2=\frac{1}{2}g(3{)}^2=\frac{9g}{2}$ ........ (2)
$e{q}^n\left(1\right)-e{q}^n\left(2\right)\Rightarrow h_B-h_A=\frac{25g}{2}-\frac{9g}{2}=\frac{16g}{2}=\frac{16\times 10}{2}=80m$