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 500 N man sitting on the scooter behind the driver manages to stay at rest with respect to the scooter without touching and other part. The force exerted by the seat on the man is