Question

Explain how can we find the work done by a variable force answer

Answer 1

Work done by variable force.

You need to understand the concept behind integrating it.

For Eg:

Q charge is kept fixed at point A. We move q charge from R1 to R2 under influence of Q charge.

Now force is variable here i.e F = KQq/r^2 , you can see, it depends on r.

So we need to understand the aspect of integrating.

Suppose we assume Force at any distance x from Q be KQq/x^2

we move q by a very little displacement dx, understand that dx is so small that we can assume force to be constant for this displacement and equal to KQq/x^2

now we can do F.dx and integrate it. This is the beauty of integration.

Remember that taking dx i.e small element makes Force constant for that dx. and we can do F.dx.

This is how we calculate work done for variable force.

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Should I tell you a easy way to do that sometimes:

use Work -Energy Theorem, it can be useful sometimes and avoid integration in some questions.