To find the average speed of the car during its total journey, we can use the formula:
Average speed = Total distance / Total time
Let's assume the total distance traveled by the car is D. Since the car covers half of the journey at a speed of 20 m/s and the other half at a speed of 30 m/s, each half is D/2.
The time taken to cover the first half of the journey at a speed of 20 m/s is given by:
Time1 = Distance1 / Speed1 = (D/2) / 20 = D / 40
Similarly, the time taken to cover the second half of the journey at a speed of 30 m/s is:
Time2 = Distance2 / Speed2 = (D/2) / 30 = D / 60
The total time taken for the journey is the sum of Time1 and Time2:
Total time = Time1 + Time2 = D/40 + D/60 = (3D + 2D) / 120 = 5D / 120 = D / 24
Now, we can calculate the average speed:
Average speed = Total distance / Total time = D / (D / 24) = 24
Therefore, the average speed of the car during its total journey is 24 m/s. Thus, the correct option is c) 24 m/s.