Short-cuts For Time & Distance Problems

1. Speed, v = s/t. where s = Total distance, t = Total time

2. The relative velocity of two bodies moving at velocities u and v (u>v) in the same direction is (u – v).

3. The relative velocity of two bodies moving in opposite directions is (u + v).

4. A train or a moving body of known length has to travel its own length in passing a lamp post or a fixed body of insignificant size.

5. A train or a moving body must travel its own length plus the length of the stationary body in question, if the train or the moving body has to pass a stationary body i.e. a bridge, a railway platform etc.

6. Motion downstream or upstream:
Velocity of boat downstream = (u + v)
Velocity of boat upstream = (u – v)
Where ‘u’ is the velocity of the boat in still waters and ‘v’ is the
velocity of the stream.

7. If a man changes his speed in the ratio u : v, the corresponding ratio of times will be v : u