Question

if a stationary bus was suddenly speed up passenger are thrown in backward direction why is it so

If it is because of inertia then which type of inertia

Answer 1

This is due to inertia of rest of upper part of the passengers body when the bus or train suddenly starts moving, The lower part of the passenger’s body starts moving along with the bus or train while the upper part of the body has a tendency to remain in the state of rest due to inertia of rest, and hence falls backwards.