A Physics teacher explains the concept of relative velocity to her students in class. She emphasises that when two bodies are moving in opposite directions, their relative velocity is sum of the velocities of the two. And when two bodies are moving in the same direction, their relative velocity is difference of the velocities of the two. Students are confused. The teacher then takes two balls one red and the other green. She says suppose red ball moves with a velocity `5 m//s` and green ball moves with a velocity of `4 m//s` from a common point, and along the same straight line. if red ball is moving to the right and green ball is moving to the left, then after `1 sec`, red ball is at `R'`, where `R R' = 5 m` and green ball is at `G'` where `G G' = 4 m`, Figure. The distance between the two balls after `1 sec = G' R' G G' + R R' = (4 + 5) = 9 m`.
This is the magnitude of their realtive velocity. If both the balls are moving to the right, as shown in Figure. The distance between the two balls after ` sec = G' R' - G G' = 5 - 4 = 1 m`.
In that case, relative velocity `= 1m//s`.
(a)
Read the above passage and answer the following questions :
(i) What value has the Physics teacher displayed ?
(ii) What have the students picked up ?
(iii) Give atleast one practical example of the concept.

Explanation

(i) The Physics teacher has displayed that giving practical illustration is a better way of driving home a difficult concept.
(ii) The students have picked up that learning is faster and more lasting with practical demonstration. And they should themselves follow this technique in their day to day life.
(iii) In practice, we find that head on collisions are far more disastrous than the collisions when two vehicles are moving in the same direction. This is because in the formerc case, relative velocity of vehicles is much larger than their relative velocity in the latter case.