Question

Why do passengers in a bus tend to fall backward when it starts suddenly?

Answer 1

See, this is basically due to the inertia of rest.
Inertia of rest just means that if a body is at rest then it will tend to resist any type of change in its state.
So here our legs are connected to bus so our legs moves forward but our upper half has inertia of rest and due to that it resist the movement of the bus and tends to remain in the earlier rest position only which ultimately results in us falling backwards....

Hope it helps......

Answer 2

$\huge \underline{ \rm{Answer}}$

$\longrightarrow$When a passenger is sitting or standing in a stationary bus, both the bus and the passenger are at rest. When the bus starts moving suddenly,the lower part of passenger's body starts moving forward with the bus.The upper part of the body tends to remain in the position of rest due to inertia of rest.As a result, therefore,the passenger falls or leans backwards.