Question 76

A 270 m long train running at a speed of 120 km/h crosses another train running in opposite direction at the speed of 80 km/h in 9 seconds. What is the length of the other train?

Solution

let first train be a and second train be b

length of a = 270 m

speed of a= 120 km/hr = $$120\times{\frac{5}{18}}$$ = $$\frac{100}{3}$$ m/sec

speed of b = 80 km/hr = $$80\times{\frac{5}{18}}$$ = $$\frac{200}{9}$$ m/sec

average speed = $$\frac{100}{3}$$ + $$\frac{200}{9}$$ = $$\frac{500}{9}$$

$$\frac{270 + x}{\frac{500}{9} }$$ = 9

270 + x = $$9\times\frac{500}{9}$$

x = 500 - 270

x = 230 m

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