A racing car accelerates uniformly through three gear changes with the following average speeds:20 ms-1 for 2.0s ;40ms-1 for 2.0 s and 60 ms-1 for 6.0s. What is the overall average speed of the car?

Explanation

To find the overall average speed, we use the formula: Average speed = Total distance / Total time. First, calculate the individual distances traveled during each gear change:For the first gear change: Distance = 20 ms-1 x 2 s = 40 mFor the second gear change: Distance = 40 ms-1 x 2 s = 80 mFor the third gear change: Distance = 60 ms-1 x 6 s = 360 mThe total distance is 40 m + 80 m + 360 m = 480 m. The total time is 2 s + 2 s + 6 s = 10 s. Thus, the overall average speed is 480 m / 10 s = 48 ms-1, making Option D the correct answer.Options A, B, and C are incorrect because they do not correctly apply the formula for average speed, either due to incorrect calculations or by using incorrect values.