A car travels 100 km at a speed of 60 km/h and returns with a speed of 40 km/h. Calculate the average speed for the whole journey.
In the first case, car travels at a speed of 60 km/h for a distance of 100 km
In the second case, car travels at a speed of 40 km/h for a distance of 100 km
Total distance travelled = 200 km
In the first case, car travels at speed of 60 km/h for a distance of 100 km
Speed = \(\frac{Distance}{Time}\)
Time = \(\frac{Distance}{Speed}\)
\(t_1 = \frac{100}{60}\)h
In the second case, car travels at a speed of 40 km/h for a distance of 100 km
\(t_2 = \frac{100}{40}h\)
Total distance travelled = 200 km
Total time taken = \(\frac{100}{60}\) + \(\frac{100}{40}\)
Average speed = \(\frac{Total\;distance\;travelled}{Total\;time\;taken}\)
= \(\frac{200}{\frac{100}{60} + \frac{100}{40}}\)
= \(\frac{2}{\frac{1}{60} + \frac{1}{40}}\)
= \(\frac{240}{5}\) = 48 km/h