Question

A runaway train car that has a mass of 11,000 kg travels at a speed of 4.5 m/s down a track. Compute the time (in s) required for a force of 1000 N to bring the car to rest.

I got 45 m/s but my homework is saying I got it wrong.

Answer #1

Given the mass of the train m = 11000kg

The force acting on the car is F = 1000 N

By Newton's second law of motion, the magnitude of the acceleration of the car is

Since the car is decelerating, the acceleration of the car is negative.

Initial velocity of the car is v_{i}=4.5 m/s

Final velocity of the car is v_{f}=0

Since the acceleration of the car is constant, the motion of the car is governed by the kinematics equations for uniformly accelerated motion. To find the time in which the change in velocity occur we use

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