Question

Solve this:

23. A body of mass 1 k is thrown upwards with a velocity 20 m/s. It momentarily comes to rest after attaining a heigh o 18 m. How much energy is lost due to air friction ? (g=10 m/s²)

1) 30 J
2) 40 J
3) 10 J
4) 20 J

Answer 1

First we find out the height up to which body will reach in the absence of air,

using conservation of energy,

1/2 mu²= mgh

h = u²/2g = 20 m

In the presence of air it was raised up to 18 m. So (20 m-18 m=2 m) distance difference is due to air-drag. Hence the work done by air-drag is,

=mgh=1 x 10 x 2=20 J