## Tuesday, September 2, 2008

### Newton’s Laws of Motion –Study Plan - Session 2

Day 2 Study Plan

5.2 Newton's second law
5.3 Working with Newton's laws

W.O.E. 3 and 4

5.2 Newton's second law

The acceleration of a particle as measured from an inertial frame is given by the (vector) sum of all the forces acting on the particle divided by its mass.

a = F/m or F = ma

Acceleration and force are measured at the same instant. If force becomes zero at an instant, acceleration also becomes zero at the same instant.

5.3 Working with Newton’s First and Second Law

1. Decide the System

We have to assume that forces are acting on a system and the system is at rest or in motion. In this context, the system may be a single particle, a block, a combination of two blocks one kept over the other or two blocks connected by a string etc. But there is a restriction for treating one as a system. All parts of the system should have identical acceleration.

Step 2. Identify the Forces

Once the system is decided, make a list of the forces acting on the system due to all the objects other than the system. Any force applied by the system should not be included in the list of the forces (material from the chapter on forces should help you in deciding various forces exerted by the system and forces exerted by the objects on the system).

Step 3. Make a Free Body Diagram

Represent the system by a point in a separate diagram and draw vectors representing the forces with this point as the common origin

Step 4: Choose axes and Write Equations.

Example 5.2

The example describes a block being pulled by a man with help of a string.
The system under analysis is the block.
It is accelerating in the horizontal direction. So there is net force in the horizontal direction.
It is not accelerating in the vertical direction. Hence net force is vertical direction is zero.

Worked out examples:
3,4,5,

Obective I

3,5, 6,9,10,

Attempt questions in Objective questions (OBJ II)

4

Exercises

1, 2, 3,