Question

Give reason person travelling in a bus tends to fall backwards, when it start suddenly

Answer 1

$\bold {Answer:}$ When the bus starts moving suddenly, the lower part of the body of passengers, which is in contact with the bus, come in motion, but upper part of their body tends to be in the state of rest and the passengers fall backward.

Answer 2

its all happens for moving interia

according to Newton's 1st law