Question

A car traveling at a speed of 24 m/s comes to a stop at a red light. How much time will it take for the car to stop if its acceleration is –8.0 m/s2? 3 s 16 s 32 s 192 s

Answer 1

Via kinematic equations we have:

$v_{final}=v_{initial}+at$

In this case since the car will stop the final velocity is 0, the initial velocity is 24 m/s and the acceleration is -8 m/s^2.  Therefore, we need to isolate the time variable (t) and so:

$0=24\frac{m}{s}+(-8\frac{m}{s^2})t\\\\0-24\frac{m}{s}=-8\frac{m}{s^2}t\\\\\frac{-24\frac{m}{s}}{-8\frac{m}{s^2}}=t \\\\t=3s$

The car would come to a complete stop in 3 seconds.

Answer 2

Answer;

3 seconds

Explanation;

Acceleration is the rate of change in linear velocity.

Acceleration = (final velocity -initial velocity) /time

In this case;

Final velocity = 0 m/s (because the car is going to rest by stopping)

Initial velocity = 24 m/s

Acceleration = -8.0 m/s²

Thus; - 8.0 m/s² = (0-24 m/s)/ t

           time = (-24 m/s)/-8.0 m/s²

                     = 3 seconds