Question

A body of mass 1kg falls from a height of 30m if it reaches the ground with speed 20 m /s then work done by air resistance is

Answer 1

From Work-Energy Theorem

W1 +W2 = ∆KE
___________________________
| W1= Work done by weight = mgh
|
| W2= Work done by air =???
|
| ∆KE = Change in K.E= 1/2 mv^2
___________________________

We have. to find work done by Air

so

W2 = ∆KE - W1

===1/2 m×v^2 - mgh

=== (1/2 ×1×20×20)- (1×10×30)

=== 200 - 300

W2= - 100 J


so work done by air is -100 joule.