The speed of a train is 156 km/h.  It crosses a tunnel in 45 seconds and overtakes a person walking at a speed of 12 km/h in the same direction in 15 seconds.  The length (in m) of the tunnel is?

1350 m

Length of train = l_t

Relative speed = 156 - 12 = 144 km/h

l_t = 144 × \(\frac{5}{18}\) × 15 = 40 × 15 = 600 m

600 + L_Tunnel = 156 × \(\frac{5}{18}\) × 45 = 26 × 5 × 15 = 1950

 L_Tunnel = 1950 - 600 = 1350 m