A body of mass $2 \mathrm{~kg}$ thrown vertically from the ground with a velocity of $8 \mathrm{~ms}^{-1}$…
A body of mass $2 \mathrm{~kg}$ thrown vertically from the ground with a velocity of $8 \mathrm{~ms}^{-1}$ reaches a maximum height of $3 \mathrm{~m}$. The work done by the air resistance is (acceleration due to gravity $=10 \mathrm{~ms}^{-2}$ )
4J
60J
64J
8J
Solution
Initial energy of particle
$
=\frac{1}{2} m v^2=\frac{1}{2} \times 2 \times 8^2=64 \mathrm{~J}
$
Final energy of particle at maximum height
$
=m g h=2 \times 10 \times 3=60 \mathrm{~J}
$
Work done against air friction
$
=\text { Loss of energy }=64-60=4 \mathrm{~J}
$