Q8: Prb 3 - Compute the time required, in seconds, for a force of 1350 N to bring the car to rest.

Question

A runaway train car that has a mass of 13500 kg travels at a speed of 5.5 m/s down a track.

Answer 1

We can calculate the acceleration of the the train car by rearranging the equation F = ma to solve for acceleration a when a known force F is applied to an object of known mass m. The direction of the force shall be negative, given that the initial speed is + 5.5 m/s and the force shall bring the train to rest.

a = F/m

a = (-1350 N)/(13500 kg) = -0.1 m/s²

We can use the equation v = v_i + at to solve the time t at which final velocity v is reached when an object has an acceleration of a.

v = 0 m/s

v_i = 5.5 m/s

a = -0.1 m/s²

0 m/s = (5.5 m/s) + (-0.1 m/s²)t

-5.5 m/s = (-0.1 m/s²)t

t = (-5.5 m/s)÷(-0.1 m/s²) = 55 s