Constraint Relations Made Easy 🔥 NEET Physics 2026 | Pulley Problems Fast Tricks

Hinzugefügt: 2026-05-08

[00:00:00]Hello guys, welcome to BMCC. So this particular video we will discuss about the one of the most important topic of the laws of motion that is constraint relation. So with the help of one example I'm going to illustrate this particular concept.

[00:00:16]So the word meaning of uh the constraint relation that is one one object one once one object is interlin with the other object. For the example, suppose this is one of the small rod which is placed against the vertical wall and the horizontal surface.

[00:00:40]Let l be the length of the rod.

[00:00:45]Length of rod.

[00:00:49]Now this rod starts sliding like that.

[00:00:54]general tendency of the sliding of the rod downward. So let this is A and this is B. These are the two ends of the rod.

[00:01:03]Now here what we observe the A end coming down and B moving away from this point. So the length of the Y continuously decreases and the length of the X continuously increases. So here what we see this is increasing and this is continuously decreasing but one thing remains constant that is length of the rod. This one remains constant. So what we can do here using pythagoras theorem x² + y² is equal to l² that we can do that we know since our childhood because this is fluctuating this is fluctuating but rod remains constant. So that's why we can write this relation. Now because it both both here both are moving. So it means both having some motion and which is interlin.

[00:02:00]Then we can do one thing differentiating both side with respect to time.

[00:02:13]So it is dl² by dt. And as we know differentiation of any constant is zero.

[00:02:20]So here what we can write using the formula of the differentiation dx by dt plus dy by dt which is equal to zero. You know one thing here b moving away it means velocity of b can be written as dx by dt. A is coming down so it is what?

[00:02:46]dy by dt. Now after simplifying this thing what we can write so this two gets canceled out. So x velocity of b is equal to minus y velocity of a. So this one of the particular relation that we got here which is velocity of B is equals to we can write here also - Y upon X velocity of A.

[00:03:30]So velocity of B depends on the velocity of A or interlin with the velocity of A.

[00:03:36]Similarly we can find the relation between the acceleration of the point A and the point B. So it means here basically what we are discussing and what we are going to explain here that is interlin of the velocity. So that relation is known as constraint relation. All right. Okay. Thank you. So for more videos like and subscribe this video. Thank you.