Question

A car is traveling north at 17.7m/s After 12 s its velocity is 14.1m/s in the same direction. Find the magnitude and direction of the car's average acceleration.
a2.7 m/s2, north b0.30 m/s2, south c2.7 m/s2, south d0.30 m/s2, north

Answer 1

The car is initially traveling north at 17.7 m/s, and after 12 s, its velocity is 14.1 m/s, still due north. This means that the direction of the car has not changed, so we can already say that the direction of the acceleration is north (if the magnitude of the acceleration is positive) or south (if the magnitude of the acceleration is negative).

To find the magnitude of the average acceleration, we must calculate the ratio between the change in velocity and the time taken:

$a=\frac{v_f -v_i}{t}=\frac{14.1 m/s-17.7 m/s}{12 s}=-0.3 m/s^2$

Since the acceleration is negative, it means it is in the opposite direction to the motion of the car, therefore south. Therefore, the correct answer is

b) 0.30 m/s2, south