Question

A scooter starting from rest moves with a constant acceleration for a time Δt₁. then with a constant velocity for the next Δt₂ and finally with a constant deceleration for the next Δt₃ to come to rest. A 500N man sitting on the scooter behind the driver manages to stay at rest with respect to the scooter without touching any other part. The force exerted by the seat on the man is 

(a) 500N throughout the journey 

(b) less than 500N throughout the journey 

(c) more than 500N throughout the journey 

(d) > 500N for time Δt₁ and Δt₃ and 500N for Δt₂.

Answer 1

(d) > 500N for time Δt₁ and Δt₃ and 500N for Δt₂.

Explanation: 

During the constant velocity for time Δt₂ there is no relative movement between the man and the seat and only force applied by the seat on the man is Normal Force which is equal to weight of the man =500 N. 

But during the acceleration (Δt₁) and deceleration (Δt₃) the seat exerts an addition force of friction on man in horizontal direction. Let this be F. 

Now the force by seat on man is resultant of 500 N and F, 

=√{(500)²+F²} N,  which is >500 N.