Question

A train $ A $ which is $ 120 \,m $ long is running with velocity $ 20 \,m/s $ while train $ B $ which is $ 130 \,m $ long is running in opposite direction with velocity $ 30 \,m/s $ . What is the time taken by train $ B $ to cross the train $ A $ ?

• A. $ 5\,s $
• B. $ 25\,s $
• C. $ 10\,s $
• D. $ 100\,s $

Answer 1

Answer: (A)

Length of train $ A = 120 \,m $
Velocity of train $ A $ , $ v_A = 20 \,m/s $
Length of train $ B = 130\, m $
Velocity of train $ B $ , $ v_B = 30 \,m/s $
Relative velocity of $ B $ w.r.t. $ A = v_B+ v_A = 50\, m/s $
(trains move in opposite directions)
Total path length to be covered by $ B = 130 + 120 = 250 \,m $
$ \therefore $ Time taken by train $ B=\frac{250\,m}{50\,m/s}=5\,s $