Question

5. A car is traveling at 20 0 m/s when the driver sees a child standing in the road. The

driver takes8 s to react, then steps on the brakes and slows at 5.0 ms. Once the
brakes are pressed, the car stops in an additional 4 seconds. How far does the car
travel before it stops from when the driver sees the child?

Help please !!

Answer 1

We know that

• The initial velocity is 20 m/s.

,

• The acceleration is -5 m/s^2.

,

• The final velocity is zero because it stops.

,

• The time spent to stop is 4 seconds.

Let's use the following formula.

`v^2_f=v^2_0+2ad`

Using the given magnitudes, we have

`0=20^2+2(-5)d`

Let's solve for d.

`\begin{gathered} 0=400-10d \\ -400=-10d \\ d=(-400)/(-10) \\ d=40m \end{gathered}`

Therefore, the car stops 40 meters away after stepping on the brakes.