During a car crash a 65kg person's head goes from traveling at 50km h-1 to stationary in 0.15s.

(a)What is the magnitude of the average net force acting on the head of a person with a 4.5kg head?
(b)How does this compare with the weight force acting on the person?

1 answer

50kph = (50 /3.6) = 13.89m/sec.
Acceleration = (v/t) = 13.89/0.15, = -92.6m/sec^2.
a) Average force on head = (ma) = 4.5 x 92.6, = 416.7N.
b) Weight force = (65 x 9.8) = 637N. So force on head is (416.7/637) = 0.654 of weight force.