Question

A stone is dropped from a building the height of the building is 20 m calculate the velocity of the stone when it is heated the ground

Answer 1

It will have non-uniform speed.

Its speed will be increasing from the moment it's dropped till the moment it hits the ground.

It will, however, have uniform acceleration. The rate at which the speed is increasing will remain constant throughout the fall.

The above is ignoring air resistance. If you account for air resistance, then the acceleration is not quite uniform either. The faster the stone falls, the greater the air pushes back on it.

After falling for enough time (this won't happen in just 20 meters) the stone will reach a speed where the air resistance is exerting an upward force that is equal to the downward force of gravity. At that time, the stone will stop accelerating and will then have a constant speed.

However, the above still ignores the changing density of the atmosphere. The atmosphere is thinner the higher up you go. Likewise, it is denser the closer to the earth's surface you go.

So if you take that into account, then neither velocity (speed) nor acceleration would be entirely constant.

Once the stone reaches a point where the air resistance is equal to the force of gravity, it would stop accelerating downwards. But, then it falls a little farther, and now the atmosphere is denser. That means the air resistance for the stone's current speed is now -greater- than the force of gravity.

This results in the stone having acceleration upwards! Or, negative acceleration downwards if you would prefer to think of it that way.

Basically the stone would start to slow down at that point, until the force of gravity and the force of air resistance once again balance out.

If the stone were a meteor falling from space… Then it would also be continuously losing some of it's mass as it burns and breaks apart from the heat generated by friction with our atmosphere. That would cause the force of gravity to change… But also the force of air resistance because the thing now has less surface area.

Trying to precisely calculate the fall of a meteor (or anything from space at those speeds) is probably a pain.