Work, Energy and Power Physics Notes
The words work, energy and power are very commonly used in our day to day lives. A man reading a book, a women washing clothes, a farmer ploughing his fields, all are said to be doing their work. Similarly, the energy in a person is decided on the basis of the work done by him. In the same way, a person wining a championship or boxing match is said to be very powerful.
We studied Newton’s law of motion in the previous chapter. With the help of these many problems of Mechanics can be solved. In this chapter we will study about work, energy and power, and their uses to solve the problems.
→ Work: When the force applied on any object changes the position of the object, then work done is defined as the product of the component of force in the direction of motion and the displacement; i. e.
Work = \(\vec{F} \cdot \vec{d}\) = Fd cosθ
→ Work done by variable force: For a variable force, the work done is the area under the curve between force axis and displacement axis.
→ Energy: The ability of doing work is called energy. There are various forms of energy such as sound energy, chemical energy, light energy, solar energy, nuclear energy, etc.
→ Kinetic energy: Kinetic energy is that energy which is in an object (body) due to its motion. Its value is calculated by the work done in bringing the object from zero velocity to that velocity.
→ Potential energy: It is that energy which is due to the position of the object. Its value is calculated by the force applied in moving an object (body) from one state to the other.
→ Potential energy of the spring: The potential energy of a spring is \(\frac{1}{2}\)kx , where k is spring constant.
→ Law of conservation of mechanical energy: The mechanical energy of any body or a system i. e., the sum of its kinetic energy and potential energy is constant in the presence of conservative forces. This is stated as ;
K + U = constant.
→ Conservative and non-conservative forces: A force is said to be conservative if the work done by or against the force is dependent only on the initial and final positions of the body and not on the path followed by the body. Example the gravitational force, magnetic force, etc. A non-conservative force is if the work done by or against the force is depend upon the path followed by the body.
Example friction, induction force, etc.
→ Power: The rate of doing work is called power.
→ Collision: The mutual interaction between two bodies for a short interval of time is called collision.
→ Types of collision: Collisions are of two types:
- Elastic collision: Inelastic collision both momentum and kinetic energy are conserved quantities.
- Inelastic collision: In inelastic collision the kinetic energy is not conserved but momentum is conserved.
→ One dimensional elastic collision: When before and after collision the velocity of the particles is in the previous direction then it is called one dimensional elastic collision.
→ Completely inelastic collision: The collision in which the colliding bodies stick together and move as one body after collision, is called completely inelastic collision.
→ Two-dimensional collision: When initial and final velocities lie in a plane, it is called two-dimensional collision.
→ Work: Work done is the product of component of force in the direction of motion and displacement.
→ Energy: The ability to do work is called energy.
→ Kinetic energy: The energy associated with the motion of an object is called kinetic energy.
→ Potential energy: The energy possessed by a body by virtue of its position.
→ Force constant: For any spring the force constant is that force which generates unit displacement.
→ Conservative force: A force is said to be conservative force if the work done by or against the force is dependent only on the initial and final positions of the body and not on the path followed by the body.
→ Non-conservative force: If the work done by or against the force is dependent on the path followed by the body.
→ Collision: The intt raction between two bodies for a short interval of time is called collision.