Acar moving 20 m/s in the positive x-direction slams on the brakes and stops after skidding 20 m. what was its acceleration during this period?

To find the acceleration of the car, we can use the following relationship:

where
is the final speed of the car (it is zero because the car comes to rest)
is the initial speed of the car
is the acceleration
is the distance covered

By rearranging the equation, we get:

where the negative sign means it is a deceleration.

Iwould say a is accurate