Question

when body is dropped freely it falls with an acceleration of 9.8 metre per second square and when a body is thrown vertically upwards it undergoes up of 9.8 metre square​

Answer 1

Notice that when the rock is at its highest point (at 1.5 s), its velocity is zero, but its acceleration is still −9.80 m/s2. Its acceleration is −9.80 m/s2 for the whole trip—while it is moving up and while it is moving down.

Vertical motion under gravity. When you throw an object upwards, it will eventually fall back to the ground under the earth's gravity. In fact all objects near the earth's surface fall with a constant acceleration of about 9.8 (we usually take 10 for the sake of simplicity in calculation).