Question

A stone is allowed to fall from the top of a tower 100 m high and at the same time another stone is projected vertically upwards from the ground with a velocity of 25 m/s. Calculate when and where the two stones will meet.​

Answer 1

Let the stones meet at point A after time t.

For upper stone :

u^ prime =0;

x = 0 + 1/2 * g * t ^ 2;

x = 1/2 * 10 * t ^ 2;

x=5t^ 2

For lower stone:

u = 25 m/s;

100 - x = ut - 1/2 * g * t ^ 2;

100-x=25t-5t^ 2;

100 - x = (25) * t - 1/2 * 10 * t ^ 2

Adding (1) and (2),

we get 25t = 100;

t=4s