Motion in a Straight Line

Question : 7

Total: 27

Two trains A and B of length 400 m each are moving on two parallel tracks with a uniform speed of 72 km h‌–1 in the same direction, with A ahead of B. The driver of B decides to overtake A and accelerates by 1 m s‌–2. If after 50 s, the guard of B just brushes past the driver of A, what was the original distance between them?

Solution:

For train A:‌uA=72 km h−1=20 ms−1;
t=50 s;a=0
∴‌SA=uAt
or SA=20×50
=1,000 m
For train B:‌uB=72 km h−1
=20 m s−1
t=50 s;a=1 m s−2
∴‌SB=uBt+

at2
or SB=20×50+

×1×(50)2
=2250 m
Let the original distance between the two trains be S.
S=SB−SA
or S=2,250−1,000
=1250 m

Go to Question:

Prev Question

Next Question