Question

An object is dropped from top of tower of height 80m. One second later,another object is thrown downwards with some velocity. The two objects reach the ground simultaneously.find the velocity with which the second object was thrown.

Answer 1

I am assuming that for the first particle there is no downward velocity.

So for the first particle, there is only the force of gravity acting downwards and accelerating the particle with g = 10m/s^2. Hence for the first particle

Here s = 80m. Solving for t we get t = 4s. So the first particle takes 4s of time to reach the ground.

The second object is thrown one second after but reaches the ground simultaneously. So, it takes 3s to reach the ground. For this particle also, the acceleration is g but it has an initial downward velocity (let’s say ).

So for particle two we write the same formula again,

Here, s = 80m, g = 10m/s^2, and t = 3s.

Solving for  we get, m/s.

This is the velocity with which the second object was thrown.