Question

You drive your car in a straight line at 15 m/s for 10 kilometers, then at 25 m/s for another 10 kilometers.

a. What is your average speed?
b. Choose the best explanation from among the following:
1) More time is spent at 15 m/s than at 25 m/s.
2) The average of 15 m/s and 25 m/s is 20 m/s.
3) Less time is spent at 15 m/s than at 25 m/s.

Answer 1

A) Average speed = 18.75 m/s

B) More time is spent at 15 m/s than at 25 m/s.

Step-by-step explanation:

Let the first distance be d1 and the second distance be d2.

We are given;

d1 = 10 km = 10000 m

d2 = 10 km = 10000 m

Speed; v1 = 15 m/s

Speed; v2 = 25 m/s

Now, the formula for distance is; Distance = speed x time

Thus:

d1 = v1 x t1

t1 = d1/v1 = 10000/15 = 666.67 seconds

Also,

d2 = v2 x t2

t2 = d2/v2 = 10000/25 = 400 seconds

Average speed = total distance/total time = (10000 + 10000)/(666.67 + 400) = 18.75 m/s

From earlier, since t1 = 666.67 seconds and t2 = 400 seconds, then;

More time at 15 m/s than at 25 m/s.