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

We know the equation of motion v = u+ at, where v is the final velocity, u is the initial velocity, a is the acceleration and t is the time taken.

In this case Final velocity = 4.5 m/s

Time taken = 7 seconds

Initial velocity = 0 m/s

`v=u+at\\ \\ 4.5 = 0+a*7\\ \\ a = 0.643m/s^2`

Car's average acceleration while it rolled down the hill = 0.643m/
`s^2`