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**Work Energy and Power- Notes**

**Work Energy Theorem**

The dot product of two vectors is equal to the product of the magnitude of the two vectors and cosine of the angle between the two vectors. The result of a dot product is always scalar.

Using the dot product, the work done is measured as the dot product of the force and displacement, which is equal to Fd cos q.

The work done can be positive, negative or zero depending on the values of the angle between the force and displacement, that is,q.

The work done by a force is positive when the angle between force and displacement is acute, that is, the angle is less than 90 degree.

The work done by a force is negative when the angle between force and displacement is obtuse, that is , greater than 90 degree and less than or equal to 180 degrees.

**Work done by variable Force and Potential Energy**

A variable force is a force whose magnitude or direction or both vary during the displacement of a body on which it acts.

The energy stored in a body by virtue of its position on configuration is called potential energy.