The diagram shows an arrangement to stop trains that are travelling too fast.
Trains coming from the left travel at a speed of 
. 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 
. 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 
. How far from marker 2 should marker 1 be placed?
