A boat is moving at the rate of 15.0 meters per second. It's speed is then decreased uniformly to 3.0 meters per second. It takes 4 seconds for the speed to decrease. What is the magnitude of the deceleration of the car?

-3 m/s²

Explanation:

The formula for deceleration is given as the change in speed over a period of time

Given that,

Initial speed = 15 m/s

Final speed = 3 m/s

change in speed = 3-15 = - 12 m/s

Time taken = 4 sec

Deceleration = - 12/4 = - 3 m/s²