Posted by Paula on .
David, who is 65 kg, is driving his car at a speed of 25 m/s. He sees a dog crossing the road and so he steps on the brake to avoid hitting it. His seatbelt brings his body to a stop in 0.4 s. What magnitude of force does the seatbelt exert on him?

Physics 
Steve,
The velocity changes by 25 m/s in 0.4 s, so the acceleration is
25/.4 m/s^2 = 62.5 m/s^2
Since F=ma, the force exerted is
65 kg * 62.5 m/s^2 = 4062.5 N