Solution : First of all we should note that in this problem the term 'speed' is being used in the same sense as velocity.
Here, Initial velocity of car, u = 25 m/s
Final velocity of car, v = 10 m/s
And, Time taken, t = 5 s
Now, putting these values in the formula for acceleration :
Thus, the acceleration of car is, – 3 m/s² (minus 3 m/s²).
The negative sign of acceleration means that it is retardation.
So, we can also say that the car has a retardation of +3 m/s².
