Question

When the brakes are applied to the bike the back seaters move forward why?

Answer 1

It's because of the first law motion

When the bike is moving with a velocity the back seater is riding too with that velocity but when suddenly brakes are applied the vehicles stops suddenly but the back seater is still tends to be in motion(in simple words he will take time to come rest) so he moves forward.

Answer 2

Hey mate

Here is ur answer

This is because the inertia of motion. When the brakes are applied the lower body comes in rest while the upper body still continues to be in motion due to inertia of motion. Thus when the brakes are applied to the bike the back sweaters move forward.