Question

If a stationary bus suddenly speeds up, passengers are thrown in the backward direction.

Answer 1

When passengers sit or stand in a stationary bus, they are in a state of rest. When the bus suddenly speeds up, the lower (parts of their body in contact with the bus acquire the speed of the bus. The upper parts of their body, however, continue to be in the state of rest due to inertia. Hence, they are thrown in the backward direction.