Problems may often feature bodies that move while other bodies may move or remain stationary.
Points to be noted
In such cases, the following points are to be noted.
- Objects like man, car, cycle, telegraph pole and tree are to be taken as point objects, with negligible When a train of length ‘l’ passes such an object, the distance covered while passing is equal to the length of the train ‘l’.
- Objects like train, platform and bridge have length which needs to be taken into account when approaching the When a train passes such an object of length ‘p’, the distance covered while passing is equal to the total length of the train and the object, i.e., ‘l+p’. This holds true even when the second object is another train.
- When two bodies pass each other (one body may be stationary), the speed of passing is equal to the relative speed between the two bodies.
Formulae related to passing, crossing and overtaking bodies
The basic formula to be applied remains the same, i.e., d = s × t. Care should be taken to substitute the correct value of ‘d’ as mentioned in the above points. Also, ’s’ should be replaced by the relative speed.
Travel and meeting
- When two persons start from two points at the same time and travel towards each other, the time taken by each of them to reach the meeting point is the Hence, the distances covered by them from their respective starting points to the meeting point will be proportional to their respective speeds.
- Assume A and B start simultaneously with speeds sA and sB respectively from points P and Q towards each other. They meet on the way at some point of time. From then onwards, A takes a time ta and B takes a time tb to reach Q and P respectively by continuing their onward travel. Then the following relationship is present between the speeds and times: