A car accelerates uniformly from rest to a speed of 20 m/s at the end of 1 min; it then accelerates uniformly to a speed of 40 m/s at the end of the next minute.During this 2-min period,the average speed of the car is
A)7.5 m/s
B)30 m/s
C)15 m/s
D)20 m/s
E)40 m/s

Question

Quizplus · Accepted Answer

The average speed is the total distance divided by the total time. The car accelerates from 0 to 20 m/s in the first minute and from 20 m/s to 40 m/s in the second minute. The average speed for each minute is the average of the initial and final speeds for that minute. So, (0+20)/2 = 10 m/s for the first minute and (20+40)/2 = 30 m/s for the second minute. The overall average speed is (10 + 30)/2 = 20 m/s.

A Car Accelerates Uniformly from Rest to a Speed of 20