summarize the chapter work and energy in 2 pages
Class9
CBSE
Plz its urgent
Answers
Answer:
Introduction to work
As you all know, in daily routine we do a lot of work like cooking, bathing, studying, carrying bag and lots more. But do you know that actually all of these do not fall in the category of work but are activities. In this chapter we will try to learn a lot about work.
Work is said to be done only when applied force produces motion. This means that for work to be done, one needs to apply force and motion has to be produced in a body.
Definition of work
Work can be defined as: Work is done when force is applied which causes displacement in the body in its own direction.
Factors on which force depends
W ∝ F
W ∝ S (Displacement).
Or W ∝ F.S
W = k .F. S
Where k is constant and its value is = 1.
Work is a scalar quantity as it specifies only magnitude not direction.
Explanation:
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Question:⤵
Summarize the chapter work and energy in two pages in notebook. Class9
Answer:⤵
Work And Energy Class 9 CBSE Notes -
Work Done
Work done on an object is defined as the product of the magnitude of the force acting on the body and the displacement in the direction of the force. W = F.s
If a force acting on a body causes no displacement, the work done is 0. For example, pushing a wall.
Energy
Energy is defined as the ability to do work. Its unit is the same as that of work.
SI unit of energy or work = Joule (Nm) or Kgm2s−2.
Energy has different forms: Light, heat, chemical, electrical or mechanical.
Mechanical energy is the sum of:
(i) Kinetic energy (K.E)
(ii) Potential energy (P.E)
Kinetic Energy
Objects in motion possess energy and can do work. This energy is called Kinetic Energy.
F = ma.
Also W = F.s
⇒ From the 2nd equation of motion v2−u2=2as,⇒ we get s = v2−u22a ⇒Substituting equation for work done by a moving body,⇒ we get W =m.a * v2−u22a
Or
⇒ Kinetic Energy = K.E= 12 mv2 (taking initial velocity u=0)
When two identical bodies are in motion, the body with a higher velocity has more K.E.
Work-energy theorem
The work-energy theorem states that the net work done by a moving body can be calculated by finding the change in KE.
⇒ W net = KE final − KE initial
⇒ Wnet= 12 m[v2−u2]
Factors affecting kinetic energy
Mass
Velocity
Momentum
Potential Energy
Energy can get stored in an object when work is done on it.
For example, stretching a rubber string. The energy that is possessed by a body by virtue of its configuration or change in position is known as Potential Energy.
Types of Potential Energy.
The potential energy of an object at a height.
When an object is raised to a certain height, work is done against gravity to change its position.
This energy is stored as Potential Energy.
⇒W = F.s
⇒F = ma
In the case of increasing the height, F = mg
Therefore , W (P.E) = mgh
⇒ ΔPE=mg(h final−h initial)
Law of Conservation of Energy
Law of conservation of energy states that energy can neither be created nor destroyed, but can be transferred from one form to another.
The total energy before and after the transformation remains constant.
Total energy = KE + PE
For example: consider a ball falling freely from a height.
At height h, it has only PE = mgh.
By the time it is about to hit the ground, it has a velocity and therefore has KE= 12 mv2.
Therefore, energy gets transferred from PE to KE, while the total energy remains the same.
Power
The rate of doing work or the rate of transfer of energy is called power.
It is denoted by P
⇒ P = Wt
SI unit is Watt (Js−1).
Average power = Total energy consumed/Total time taken.
The commercial unit of power is kWh i.e. energy used in 1 hour at 1000 Joules/second.
1kWh=3.6×106J
Explanation:⤵
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