Question 20

A helicopter flies along the sides of a square field of side length 100 kms. The first side is covered at a speed of 100 kmph, and for each subsequent side the speed is increased by 100 kmph till it covers all the sides. The average speed of the helicopter is

Solution

The time taken to travel each side:

1st side: $$T\ =\ \frac{100}{100}=1hr$$

2nd side: $$T\ =\ \frac{100}{200}=0.5hr$$

3rd side: $$T\ =\ \frac{100}{300}=0.33hr$$

4th side: $$T\ =\ \frac{100}{400}=0.25hr$$

Average speed = $$\frac{\text{total distance}}{\text{total time}}$$ = $$\frac{400}{1+0.5+0.33+0.25}=192.3$$

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