Question

An auto travels at the rate of 25 km/h for 4.0 minutes, then at 50 km/h for 8.0 minutes, and finally at 20 km/h for 2.0 minutes. Find (a) the total distance covered in km and (b) the average speed for the complete trip in m/s.

Answer 1

(a) We use the formula,

`Distance = speed * time`

The total distance covered by auto,

`= 25 \ km/h * ( 4.0 \ minutes * (1 \ h)/(60 \ minutes ) )  + 50 \ km/h * ( 8.0 \ minutes * (1 \ h)/(60 \ minutes )) + 20 \ km/h * ( 2.0 \ minutes * (1 \ h)/(60 \ minutes ) ) \\\\ = 9.1 \ km`

(b)

Average speed = total distance / total time

Total time = 4/60 + 8 /60 + 2/60 = 14 /60

Thus, average speed

`= (9.1)/((14)/(60) ) =39 \ km/ h`

Average speed in m/s,

`39 \ km/ h = (39 * 10^3 \ m)/(60 * 60 s) = 10. 83 \ m/s`