Question

From a tower of height 20m, a boy throws a stone in the vertically upward direction with a velocity of 40 m/s and at the same time a girl drops another identical stone from the same tower. When the momentum of the stone dropped by the girl is maximum, what will be the displacement of the stone projected in the upward direction

• A. 60 m
• B. 40 m
• C. 20 m
• D. 0 m

Answer 1

The correct option is A 60 m

Time of flight of the stone dropped by the girl.
$S=ut+\frac{1}{2}a{t}^2$ $\because u=0$
$+20=+\frac{1}{2}\times 10\times t^2$
$t^2=4\Rightarrow t=2s$
Displacement of the stone thrown by the boy in the upward direction at
t = 2s
$S=ut+\frac{1}{2}a{t}^2$
$S=40\times 2-\frac{1}{2}\times {10}^5\times 4$
S = 80 - 20 = 60 m
S = 60 m