The Fly


A fly is flying between two trains, each travelling towards each other on the same track at 60 km/h. The fly reaches one engine, reverses itself immediately, and flies back to the other engine, repeating the process each time. The fly is flying at 90 km/h. If the fly flies 180 km before the trains meet, how far apart were the trains initially?

For Solution SCROLL DOWN...


Initially, the trains were 240 km apart.

The fly is flying at the speed of 90 km/h and covers 180 km. Hence, the fly flies for 2 hours after trains started. It's obvious that trains met 2 hours after they started travelling towards each other. Also, trains were travelling at the speed of 60 km/h. So, each train traveled 120 km before they met. Hence, the trains were 240 km apart initially.


Anonymous said...

240 kms....................rajesh

Anuj said...

240 KM

Anonymous said...

Relative Velocity between trains

Vr = Vt1 + Vt2 = 120km/h

Given Vf = 90km/h
Distance travelled by fly Sf = 180km/h

Sf = Vf * Tf
--> tf = 180/90 = 2 hrs;

So fly flew for 2 hrs.,

since at Tf 2 trians met each other
St = Vr * tf

St = 120 * 2 = 240 Km

so, trains are initially separated by 240 km

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