Laws of Motion- FAQ in JEE Mains

Laws of Motion

Laws of Motion is one of the major topics in physics as it lays the foundation for the entire mechanics. Let’s take a look at a few FAQ’s related to the topic.

1. What are the major concepts involved in the topic?

The major concepts involves: Frame of reference, Newton’s First law of motion (Law of Inertia), Newton’s Second law of motion, Newton’s Third law of motion (For every action there is an equal and opposite reaction) and constraint equations.

2. What are the characteristics of Normal Force?

Normal force is an electromagnetic force and always acts perpendicular to the surface of contact. For example,

3. What do we understand by Free Body Diagram?

A free body diagram represents all the forces acting on the body. For example,

So, the FBD for sphere B will be as shown below,

4. What are steps to solve a problem on Newton’s laws of motion?

Let’s take the following example,

The wedge is fixed and we need to find the acceleration of the block of mass m along the incline.

Step 1: Draw the F.B.D of the block,

Step 2: Writing the force equation taking our own axis, in this case, we take two axes one along the plane and the other perpendicular to it.

Fincline = \(mg~ sin45^{circ}\)

VFNormal = \(N ~–~ mg~ cos45^{circ}\)

Step3: Calculating acceleration using second law of motion

\(mg ~sin45^{circ}\)  = \(ma\)

  • \(a\) = \(g~ sin45^{circ}\)

5. What is constraint equation?

  When the motion of one body is governed by another or in other words when the motion of two or more bodies is interlinked. The equation governing such motion is known as constraint equation. For example:

If we draw the FBD and write equations we will get,

\(M_1.g ~–~ T\) = \(M_1.a_1\)

\(2T – M_2.g\) = \(M_2.a_2\)

We can see there are two equations and three unknowns: \(a_1\), \(a_2\) and \(T\). So we need one more equation and that will be the constraint equation.

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Practise This Question

All natural numbers are whole numbers.