Paper 2 · November 2023 · conservation of linear momentum; impulse and force; circular motion

A car travelling at 20 m/s hits a large rock and stops instantly. A passenger of mass 65 kg wearing a seat belt is brought to rest in 0.5 s. Calculate the magnitude of the constant force the belt exerts on the passenger.

Model answer

2600 N

Also accepted: 2.6 x 10^3 N, 2600

Explanation

The belt has to remove the passenger's momentum

p = mv = 65 \times 20 = 1300

kg m/s in 0.5 s. Force is the rate of change of momentum, so

F = \Delta p / \Delta t = 1300 / 0.5 = 2600

N. The force acts backwards, opposite to the car's original motion.

Derived from ZIMSEC Physics Paper 2, November 2023, Q1

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