JEE Main Work, Energy and Power Revision Notes

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When a constant force F is applied on the box upon the smooth surface, at a certain point of application, it offers a displacement s. 

Mathematically, it can express as W = F s cos Θ

(Image to be added soon)


Θ = the angle between F and s (displayed in the above image)

Here, F cos Θ plays an important role in the work done.

  • Role of Gravity in Work Done

The work done by gravity is said to be negative if an object is moving in an upward direction. The expression for the statement is, 

Wg = - m.g.h

Note: Work done is positive when it is falling from certain heights.

  • Role of Friction in Work Done

A concept is always there in our mind that the force of friction results in a negative work. However, as per the observation, it is concluded that the work done by friction may be zero, positive, negative or zero according to the condition. 

  • Role of  a Variable Force in Work Done

If there is a chance of any alteration or variation of magnitude and direction of a force in a three-dimensional space, the expression can be obtained as a function of the position vector F. 

Consider that a force is present in 3 – D space. Also, assume that the force’s magnitude as well as direction changes for some reason. 

The coordinates are (x, y, z) for this force F. 

We can write the work done formula as

\[\overrightarrow{F}\] . \[\overrightarrow{ds}\] = dW

JEE Main Work Energy and Power Revision Notes part-1
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FAQ (Frequently Asked Questions)

1. Why is the Force of Gravity Negative?

It has been proven that acceleration due to gravity is always negative. When an object is in its free-falling state, it has been affected only by gravity, which is - 9.81 m/s2 irrespective of the direction.

2. is the Delivered Power Negative?

According to the research, the total power transported to a circuit is equal to the total power absorbed. It has been proven that the power delivered is a negative quantity and power absorbed is a positive quantity

If we deeply study the laws of conservation of mass, it suggests that the total power of all elements in a circuit results in zero.

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