Question

An aeroplane travels a distance in the form of a square with the speeds of 400 km/hr. 600 km/hr, 800 km/hr and 1,200 km/hr respectively. Find the average speed for the whole distance along the four sides of the square.

• A. 640 km/hr
• B. 620 km/hr
• C. 630 km/hr
• D. 650 km/hr

Answer 1

Answer: (A)

640 km/hr

Let the each sides of square be$s$

Total distance$=4s$

Time taken to cover one side $=\frac{s}{v}$

Average speed = $\frac{Totaldistance}{Totaltime}=\frac{4x}{\frac{x}{400}+\frac{x}{600}+\frac{x}{800}+\frac{x}{1200}}$
= $\frac{4}{\frac{6+4+3+2}{2400}}=\frac{4\times 2400}{15}=640$km/hr.