Question

A runaway train car that has a mass of 13,000 kg travels at a speed of 6.0 m/s down a track. Compute the time (in s) required for a force of 1000 N to bring the car to rest.

Answer 1

To solve this problem, we will use Newton's second law from which force is defined as the product between mass and acceleration. Since acceleration is the change in velocity with respect to time, we will make such a representation, therefore, the formula to find the net force is

`F_(net) = m(\Delta v)/(\Delta t)`

Here

`\Delta v` = Change in speed

`\Delta t` = Change in time

The object ends at rest, therefore the final speed is 0 and the initial speed 6.0m / s, so the absolute change of speed would be

`\Delta v = v_2-v_1`

`\Delta v =|0-6| = 6m/s`

Rearranging to get the time

`\Delta t = (m\Delta v)/(F_(net))`

`\Delta t = ((13000)(6))/(1000)`

`\Delta t = 78s`

Therefore the time required to bring the car to rest is 78s