A car starts from rest and reaches 20 m/s in 10 seconds. the average acceleration of the car in m/s2 is:

In order to find acceleration, you must do change in speed divided by the time taken. In this case, the car starts from rest which is 0m/s and reaches 20m/s which is a difference of 20m/s in speed. The time taken was 10 seconds so you do 20m/s : 10 = 2m/s²