A train 540 m long is running with a speed of 72 km/hr. In what time it pass a tunnel 160 m long?

∵ Speed of the train = 72 km/hr = 72 x (5/18) = 20 m/sec.
Sum of the length of the train and tunnel = 540 + 160 = 700 metres.
∴ Required time taken to pass the tunnel = Time taken to cover 700 metres at 20 m/sec.
= 700/20
= 35 sec.