Hannah, who has a mass of 65 kg, is riding at 25 m/s in her sports car when she must suddenly swerve off the road to avoid hitting a dog and slams into the guard rail. Her seatbelt brings her to a stop in 0.4 seconds. What amount of force was
exerted on Hannah?
4000 N
4063 N
650 N
O N

Hannah comes to a rest in t = 0.4 s, so her acceleration is

a = (0 - 25 m/s) / (0.4 s) = -62.5 m/s²

(that is, the acceleration points in the direction opposing her movement forward as she brakes)

Then the force exerted on her by the seatbelt has magnitude

F = (65 kg) (62.5 m/s²) = 4062.5 N ≈ 4063 N