Question

A car drives to the east in a time of 4 hours. Then, immediately (not realistic, but just assume this is the case for this problem), travels 12 km to the west in 4 hours. The average speed for the entire trip is 5 km/hr. What is the average speed of the car for the first part of the trip, in km/hr, while the car was traveling east?

Answer 1

Answer:

Average speed in east direction $speed=\frac{distance}{time}=\frac{28}{4}=7km/hr$            

Explanation:

We have given average speed of the entire trip = 5 km/hr

First the car 4 hours then travels 12 km in 4 hours

So total time of the trip = 4+4 = 8 hours

So total distance traveled in the trip $d=speed\times time = 5\times 8=40km$

As the car travel 12 km in 4 hours to the west

So distance traveled in 4 hour in east = 40 -12 = 28 km

Time in east direction = 4 hour

So average speed in east direction $speed=\frac{distance}{time}=\frac{28}{4}=7km/hr$