Now, speed of bus in X to Y-direction observed by man=v−u and speed of bus in Y to X-direction observed by man=v+u Buses moves in either direction with equal speedv and at equal time intervals T. So, distance between buses coming from either direction is same. So, speed × time = speed × time (X to Y)(Y to X) ⇒‌(v−u)t1‌=(v+u)t2 ⇒‌v(t1−t2)‌=u(t1+t2) ‌ or ‌‌u‌=‌
v(t1−t2)
t1+t2
Hence, distance D between any 2-buses is D‌=(v−u)t1 ‌=(v−‌
v(t1−t2)
t1+t2
)t1 ‌=v(‌
t1+t2−t1+t2
t1+t2
)t1 D‌=v(‌
2t1t2
t1+t2
) Hence, time interval between any 2-buses is T‌=‌