Time and Distance – Important Shortcuts and Notes:

1. 1 Kmph = (5/18) m/s
2. 1 m/s = (18/5) Kmph
3. Speed(S) = Distance(d)/Time(t)
4. Average Speed = Total distance/Total Time = (d1+d2)/(t1+t2)
5. When d1 = d2 , Average speed= 2S1S2/(S1+S2), where S1 and S2
are the speeds for covering d1 and d2 respectively
6. When t1 = t2 , Average speed = (S1+S2)/2, where S1 and S2 are
the speeds during t1 and t2 respectively
7. Relative speed when moving in opposite direction is S1 +S2
8. Relative speed when moving in same direction is S1 – S2
9. A person goes certain distance (A to B) at a speed of S1 kmph and returns back (B to A) at a speed of S2 kmph.
If he takes T hours in all, the distance between A and B is T(S1S2/S1+S2)
10. When two trains of lengths l1 and l2 respectively travelling at the speeds of s1 and s2 respectively cross each other in time t, then the equation is given as s1+s2 = (l1+l2)/t
11. When a train of lengths l1 travelling at a speed s1 overtakes another train of length l2 travelling at speed s2 in time t, then the equation is given as s1 – s2 = (l1+l2)/t
12. When a train of lengths l1 travelling at a speed s1 crosses a platform/bridge/tunnel of length l2 in time t, then the equation is given
as s1 = (l1+l2)/t
13. When a train of lengths l travelling at a speed s crosses a pole/pillar/flag post in time t, then the equation is given as s = l/t
14. If two persons A and B start at the same time from two points P and Q
towards each other and after crossing they take T1 and T2 hours in
reaching Q and P respectively, then
(A’s speed)/(B’s speed) =sqrtT2/ sqrtT1