Acceleration Calculation:
To calculate the acceleration of the car we need to use the formula:
acceleration = (final velocity - initial velocity) / time taken
Initial velocity (u) = 20 km/h
Final velocity (v) = 60 km/h
Time taken (t) = 6 seconds

Calculation:
Substituting the values in the formula we get:
acceleration = (60 - 20) / 6
acceleration = 40 / 6
acceleration = 6.67 m/s^2

Explanation:
Acceleration is the rate of change of velocity with respect to time. In simpler terms, it is the rate at which an object's velocity changes over time. In this case, the car's velocity changed from 20 km/h to 60 km/h in 6 seconds.

The formula to calculate acceleration is (final velocity - initial velocity) / time taken. In this case, the initial velocity is 20 km/h, the final velocity is 60 km/h and the time taken is 6 seconds. By substituting these values, we get the acceleration of the car as 6.67 m/s^2.

This means that the car's velocity increased by 6.67 m/s every second. It is important to note that acceleration can be positive or negative. If the velocity of an object is increasing, the acceleration is positive and if the velocity is decreasing, the acceleration is negative. In this case, the car's velocity is increasing, hence the acceleration is positive.

Overall, acceleration is an important concept in physics as it helps us understand how objects move and change their velocity over time.