MASTER ADVANCED PHYSICS (For all Top Exams) RELATIVE VELOCITY- 1

Situation - 1 – One dimensional motion of two bodies moving opposite to each other

When two bodies are moving with velocities v1 and v2 exactly opposite to each other, then a man at the body v1 or v2 will experience a velocity that is v1 + v2.

This is a common experience when we travel in trains. When a train comes opposite to us, and crosses us, it seems to be going faster than its actual speed.

Why?

This is because WE are not stationary. While the other train is crossing us, we too are moving ahead. So, plainly, the velocities get added up by the reality of the situation!!

Situation – 2 - One dimensional motion of two bodies moving in the same direction to each other

When two bodies are moving with velocities v1 and v2 in the same direction to each other, then a man at the body v1 or v2 will experience a relative velocity that is v1 - v2.

This is a common experience when we travel in trains. When a train is gong beside us in the same direction as us, it seems to be going slower than its actual speed.

Why?

This is because WE are not stationary. While the other train is moving beside us, we too are moving ahead. So, plainly, the velocities get subtracted by the reality of the situation!!

Situational 3 – Two dimensional motion of two bodies moving at an angle to each other.

Here we simply take the relative velocity of the two bodies as the vector difference of their velocities, with respect to some origin.

V (BA) = V(BO) – V(AO)

There are many such examples, and we will see them when we do problems based on relative velocity.