Question

A driver parked his car on a steep hill and forgot to set the emergency brake. As a result, the car rolled down the hill and crashed into a parked truck. If the car was moving at 10 mph (4.5 m/s) when it hit the truck 7.0 seconds after it began to move, what was the car’s average acceleration while it rolled down the hill? Define the positive x direction to be down the hill.

Answer 1

Answer:0.642

Explanation:

Given

initially car is at rest i.e u=0

When car hits the truck it's velocity is 4.5 m/s

it hits the truck after 7 sec

Now average acceleration of car is =$\frac{change\ in\ velocity}{time\ taken}$

average acceleration of car =$\frac{\left ( final velocity\right )-\left ( initial velocity\right )}{time}$

average acceleration of car=$\frac{\left ( 4.5\right )-\left ( 0\right )}{7}$

average acceleration of car=$0.642 m/s^{2}$

Taking Down hill as positive x axis

average acceleration of car=$0.642\hat{i}$