(4) Let the length of the train be x mand the speed be y m/s. ∴
x
y
=5 ⇒ x = 5y Again length of train and bridgetogether = (x + 200) m ∴
x+200
y
=10 ⇒ x + 200= 10y ⇒ 5y + 200 = 10y ⇒ y = 200/5 = 40 ∴ Length of the train = 5 × 40 m =200 m and speed = 40 m/s ∴ Total length of the train and thetunnel is (200 + 600) m = 800 m ∴ Time required by the train tocompletely cross the tunnel =