Question

If a train takes 1.5 sec to cross a telegraph post and 1.75 to overtake a cyclist racing along the parallel road to the track at 10 m/s , then the length of the train is

Answer 1

L = length of the train = ?

t₁ = time taken to cross the telegraph post = 1.5 sec

v₁ = velocity of train

velocity of train is given as

v₁ = L/t₁  

v₁ = L/1.5                                                   eq-1

v₂ = velocity of the cyclist = 10 m/s

t₂ = time taken to overtake the cyclist = 1.75

time taken to overtake the cyclist is given as

t₂ = L/(v₁ - v₂ )

1.75 = L/(v₁ - 10 )

1.75 (v₁ - 10 ) = L

using eq-1

1.75 ((L/1.5 ) - 10 ) = L

L = 105 m