Question

an object of mass M is dropped from a height h if it strikes the ground with speed root 0.8 GH than work done by air resistance is​

Answer 1

Given:

An object of mass M is dropped from a height h if it strikes the ground with speed √(0.8gh) .

To find:

Work done by air resistance ?

Calculation:

In these type of questions, it is best to apply work energy theorem, which states : the net work done by all the forces will be equal to the change in Kinetic energy of the object.

$\therefore \: W_{gravity} + W_{air \: res.} = \Delta KE$

$\implies \: Mgh+ W_{air \: res.} = \dfrac{1}{2} M {v}^{2} - 0$

$\implies \: Mgh+ W_{air \: res.} = \dfrac{1}{2} M {( \sqrt{0.8gh} )}^{2}$

$\implies \: Mgh+ W_{air \: res.} = \dfrac{1}{2} M (0.8gh)$

$\implies \: Mgh+ W_{air \: res.} = 0.8(Mgh)$

$\implies \: W_{air \: res.} = 0.8(Mgh) - Mgh$

$\implies \: W_{air \: res.} = - 0.2(Mgh)$

So, net work done by air resistance:

$\boxed{ \bf \: W_{air \: res.} = - 0.2(Mgh)}$