The diagram shows an arrangement to stop trains that are travelling too fast. [Figure showing train approaching marker 1, then marker 2, with speeds 50 m s⁻¹ and 10 m s⁻¹] Trains coming from the left travel at a speed of 50ms⁻¹. At marker 1, the driver must apply the brakes so that the train decelerates uniformly in order to pass marker 2 at no more than 10ms⁻¹. The train carries a detector that notes the times when the train passes each marker and will apply an emergency brake if the time between passing marker 1 and marker 2 is less than 20 s. How far from marker 2 should marker 1 be placed?

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