aBt2 = t2 xA = VA (t - 10) = 50 (t - 10) A and Bare at same location if xB = xA t2 = 50t - 500 ∴ t2 - 50t + 500 = 0 t =
50±√2500−2000
2
= 25 ± 5 √5 t1 = 25 - 5√5 [At this time A crossed 'B'] t1 = 25 + 5√5 [ B is moving with increasing speed. This is the time when B overtakes A] ∴ Interval for which A is ahead Δt = t2 - t1 = 10√5 s = 10 √n ∴ n = 5