Question

A car travels a distance of 80 km. For the first 30 minutes it is driven at a constant speed of 80 km/h. The motor begins to vibrate and the driver reduces the speed to 40 km/h for the rest of the trip. The average speed for the entire trip is:

a) 47.5 km/h.

b) 53.3km/h.

c) 60.0 km/h.

d) 50.0km/h.

e) 40.0 km/h.

Answer 1

Average speed is defined as distance/time taken.

Here distance = 80 km

Time taken = 30 min + time for the remaining distance

Time for remaining distance = ?

In 30 min, the vehicle travels a distance of 40 km( speed x time = 80 x 0.5)

Remaining 40km in 40 km/hr speed can be traveled in 1hr.

Hence total time = 1.5 hr

Average speed = 80/1.5 = 53.33 km/hr

Answer:---> Option (b)

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