When braking, the impulse of the train decreased from 1.8 * 10 ^ 7 to 1.2 * 10 ^ 7 kg * m / s.

When braking, the impulse of the train decreased from 1.8 * 10 ^ 7 to 1.2 * 10 ^ 7 kg * m / s. What is the impulse of the friction force acting on the train when braking?

Since the impulse of force is equal to the change in the impulse of the body, the following relation will be true:
F * t = m * V – m * V0, where F * t is the impulse of force, m * V is the impulse of the train during braking (m * V = 1.2 * 10 ^ 7 kg * m / s), m * V0 – train impulse before braking (m * V = 1.8 * 10 ^ 7 kg * m / s).
Let’s calculate the impulse of the friction force:
F * t = m * V – m * V0 = 1.8 * 10 ^ 7 – 1.2 * 10 ^ 7 = 0.6 * 10 ^ 7 = 6 MN * s.
Answer: The impulse of the friction force is 6 MN * s.