A 300m long train is moving with uniform velocity of 90km/h. Find the time taken by the train to cross another train of length 700m moving with same speed in opposite direction.
Answers
Given :
▪ Length of train A = 300m
▪ Length of train B = 700m
▪ Velocity of train A = 90kmph
▪ Velocity of train B = 90kmph
▪ Trains move in opposite directions.
To Find :
▪ Time taken by train A to cross train B.
Solution :
✒ This question is completely based on concept of relative velocity in 1D.
- 1kmph = 5/18mps
- 90kmph = 90×5/18 = 25mps
✴ VA = 25mps
✴ VB = -25mps
Negative sign shows opposite direction.
✴ Relative velocity of B wrt A :
⏭ (V)BA = VB - (-VA)
⏭ (V)BA = VB + VA
⏭ (V)BA = 25 + 25
⏭ (V)BA = 50mps
▶Total path length to be covered by B :
▪ D = 300 + 700
▪ D = 1000m
✳ Time taken by train B :
→ time = pathlength/relative velocity
→ time = 1000/50
→ time = 20s
Answer:
its answer is 20 sec
Explanation:
its is based on relative but we can do it by another method.
distance travelled by ist train to cross the 2nd train =300+x
distance travelled by 2nd train =700-x
= t×s=d
for first train 300+X= 90t
X= 90t-300
for 2nd train 700-x = 90t
700-(90t-300)=90t
700-90t + 300=90t
1000=180t
change time in sec
= 180×5/18= 50
t=1000/50=20sec