A uniformly moving train of length 480 m takes 3 minutes to completely cross a platform. If the same train, with the same speed crosses a pole completely in 30 sec, then the length of the platform is -

Let length of platform be ‘y’metres.

Then, at the platform,Distance travelled = y + (length of train) = (y + 480)m

Then, Speed of train = (y + 480)m / (3x60) sec = (y+480)/180 ...(1)

Also, at the pole,Distance travelled = length of train = 480m

Then, Speed of train = 480m / 30sec = 16 m/s ...(2)

Equating eq.(1) & eq.(2), we get,

(y+480)/180 = 16(y+480) = 16 x 180 = 2880

y = 2880 –480 = 2400m or 2.4 km long platform.