Question

A body of mass 2 kg falls from a height of 20 m at a place where acceleration due to gravity is $10m{s}^{-2}$, and is found to acquire a velocity of $15m{s}^{-1}$. The work done against the air resistance is:

• A. 400 J
• B. 225 J
• C. 175 J
• D. zero

Answer 1

The correct option is C 175 J

W.D ( air resis ) + W. D ( gravity ) $=\Delta K.E$
W.D (against are resistance ) $=-(\frac{1}{2}m{v}^2-mgh)$
$=-(\frac{1}{2}\times 2\times 225-20\times 10\times 20)$
$=-(225-400)$

$=175J$