Importance of Sports and Games

PHYSICS CHAP. 11 WORK AND ENERGY (FA 3)
The two conditions needed to satisfy the work being done are (i) A force should act on an object, and (ii) The object must be displaced.
If any one of the above conditions does not exist, work is not done. This is the way work is viewed in science.
Work
Let a constant force, F act on an object. Let the object be displaced through a distance, s in the direction of force. Let W be the work done. We define work to be equal to the product of the force and displacement.
Work done = Force × Displacement
W = F s = mg × s
Thus, work done by a force acting on an object is equal to the magnitude of force acting on an object is equal to the magnitude of force multiplied by the distance moved in the direction of the force. Work has only magnitude and no direction.
If F = 1 N and s = 1 m then the work done by the force will be 1 N m. Here the unit of work is newton metre (N m) or joule (J). Thus, 1 J is the amount of work done by an object when a force of 1 N displaces it by 1 m along the line of action of the force.
The work done by force can either be positive or negative. When the angle between two directions is 1800, the work done by the F is taken as negative and denoted by minus sign. The work done by force is F × (-s) or (-F × s)
Energy
An object having a capability to do work is said to possess energy. An object that possesses energy can exert a force on another object. An object that possesses energy can do work. 1 J is the energy required to do 1 J work.
Kinetic Energy -
Objects in motion possess energy. This energy is called kinetic energy. The kinetic energy of an object increases its speed.
Ek = 1/2 mv2 is the work done of an object when the initial velocity, u is 0. Or
Ek = 1/2 m (v2-u2)
Potential Energy -
The potential energy possessed by the object is the energy present in it by virtue of its position or configuration.
Potential Energy of an object at a height -
The gravitational potential energy of an object at a point above the ground is defined as the work done in raising it from the ground to that point against gravity.
W = mgh
Were ‘m’ refers to mass, ‘g’ refers to gravitational force and ‘h’ refers to height. If the gravitational force is not mentioned in the question then ‘g’=9.8 m s-2.
Law of Conservation of Energy
Whenever the energy gets transformed, the total energy remains unchanged. This is the consequence of law of conservation of energy. According to this law, energy can only be converted from one form to another; it can neither be created nor destroyed. The total energy before and after the transformation remains the same. The law of conservation is valid in all situations and for all kinds of transformations.
The sum of kinetic energy and potential energy of an object is its total mechanical energy.
Potential energy + kinetic energy = constant Or Mgh + 1/2 mv2 = constant
The decrease in potential energy, at any point in its path, appears as an equal amount of increase in kinetic energy.
Rate of doing work (Power)
Power measures the speed of work done, that is, how fast or slow work is done. Power is defined as the rate of doing work or the rate of transfer of energy.
Power = work/time
Or P = w/t
The unit of power is watt having a symbol W. 1 watt is the power of an agent, which does work at the rate of 1 joule per second.
1 W = 1 joule/ second or 1 W = 1 J s-1.
Commercial Unit of Energy
The unit of joule is too small and hence is inconvenient to express large quantities of energy. We use bigger unit of energy called kilowatt hour (kW h).
1 kW h, is the energy used in one hour at the rate of 1000 J s-1 (or 1 kW).
1 kW h = 1 kW × 1 h = 1000 W × 3600 s = 3600000 J
1 kW h = 3.6 × 106 J.