Question

A car moves a distance of 200 m. It covers the first half of the distance at speed 40 km/h and the second half of distance at speed v. The average speed is 48 km/h. The value of v is

• A. 56 km/h
• B. 60 km/h
• C. 50 km/h
• D. 48 km/h

Answer 1

Answer: (B)

60 km/h

Answer 2

Total distance travelled = 200 m
Total time taken $=\frac{100}{40}+\frac{100}{v}$
Average speed $=\frac{total\, distance\, travelled}{total\, time\, taken}$
$48=\frac{200}{\bigg(\frac{100}{40}+\frac{100}{v}\bigg)}$ or $48=\frac{2}{\bigg(\frac{1}{40}+\frac{1}{v}\bigg)}$
or $\, \, \frac{1}{40}+\frac{1}{v}=\frac{1}{24}$
or $\, \, \frac{1}{v}=\frac{1}{24}-\frac{1}{40}=\frac{5-3}{120}=\frac{1}{60}$
or $\, \, v = 60\, km/hr$