Choose the positive direction of x -axis to be from south to north. Then velocity of train vT=+10ms−1 velocity of parrot vP=−5ms−1 Relative velocity of parrot with respect to train=vP−vT=(−5ms−1)−(+10ms−1) =−15ms−1 i.e. parrot appears to move with a speed of 15ms−1 from north to south ∴ Time taken by parrot to cross the train=