Question

passenger in a bus tend to fall backwards when the bus suddenly starts and tend to fall foward when it stops

Answer 1

Passenger  in  a  bus  tends  to  fall  backwards  when  the  bus  suddenly  starts    and  tends  to  fall forward  when  it  stops because   there may  a  centrifugal   force  .

Answer 2

this is because the inertia of rest and inertia of motion of the body.. respectively
in a simple language..Inertia is the resistance offered by the body whenever its state of motion is changed... that's why this happens..:))