ICE train

German runways test a new ICE train between Munich and Berlin. The train runs to Berlin at a slow speed of 110 km/h. Back from Berlin goes faster. How quickly did the train have to go on a return trip so that the average train speed for both journeys would be 200 km/h? (The task is from the customer magazine of German Railways)

Correct answer:

v =  1100 km/h

Step-by-step explanation:

v1=110 km/h v2=200 km/h  t1 = s/v1 t2 = s/v v2 = 2s /( s/v1 + s/v) v2 = 2 /(1/v1 + 1/v)  1/v1 + 1/v = 2/v2  v=2/v21/v11=2/2001/1101=1100 km/h

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Showing 1 comment:
Dr Math
infinite speed is due that train goes first half at 100 km/h so it cannot achieve average speed 200 km/h, only if second half from Munich take 0 seconds (faster that speed of  light)

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