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How to Approach Torque Problems in JEE

Torque: A measure of how much a force acting on an object causes that object to rotate.

One of the most complicated concepts in the IIT JEE syllabus is Torque and Rotational Motion. It is one of the favorite topics of examiners. So what makes Torque a favourite and why is it asked almost regularly?

Why is it a Favourite?

Rotational Motion is one of the most asked topics from mechanics in Physics. This can be attributed to the fact that through a question of rotational motion, students’ concept in friction, kinematics, circular motion can be put to test. All through one problem. This is also the reason for their higher weightage. Other than this, rotational motion problems can test a students temparament towards the problem by introducing motion in more than one axis. Among many other reasons, the most convincing probably is the amount of applicaiton it has in real life. One of the most applied topics in the entire physics today is the conservation of angular momentum. Be it an automobile or a Gymnastics, Rotational motion is a hit.

A classic example given while introducing the concept of torque to students is the ‘Door Knob’ logic . Door knobs are located on the opposite side of the hinges so that the door could be accessed using minimum force with maximum impact: a reasoning which could only be explained by the concept of Torque or Rotational Force. Because the torque required will be same for both the positions, but the force will be lesser when the distance from axle is more. Understanding the concept itself involves basic knowledge of mechanics. Since JEE examiners have always asked questions based on multiple concepts, Torque becomes a viable option to test the student’s understanding capacity.

How to tackle The Beast

To get a better grip on the problems involving Torque & Rotational Motion, there are a few simple steps you could follow:

  1. Divide and Rule:Divide and Conquer works fabulously even in the fields of science. Learn to divide the problem into logical segments and solve them independently so that the net force is according to the logic in the question. One such division can be in linear & rotational motion.
  2. Free Body Diagram: Always draw a Free Body Diagram suring any problem in mechanics. You can’t solve the problem without that. JEE always tempts to do this but you should never fall for it.
  3. Label the Values: Label the force, torque, acceleration and other variables mentioned in the questions along with the dimensions in the free body diagram. Once you do this, you’ll find out what variables aren’t mentioned and need to be worked on.
  4. Write the Force Equation: The force equation along with the momentum balance equation and other equations, when solved simultaneously, gives you the unknown variables.
  5. Write the Torque Equation: Once you’ve identified the forces, you’ll get an idea about the torque equation. Solve all the equations simultaneously and you’ll end up solving the problem or component of a problem instead.
  6. Write Conservation Equations: The problems csn frequently test you on your conservation equations i.e. Energy & Momentum conservation. Momentum here refers to both Linear and angular momentum.
  7. Solve it: Analyse all the equations, known and unknown variables logically so that substitutions, when added up, lead to the complete solution.

The most important aspect of concepts discussed in mechanics is revision so that you don’t forget the basics. Keep practicing regularly and solve as many problems as possible to sharpen your grip over the subject. Most importantly, you should keep solving sample question papers. Here is why.

All the best!

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