Question

A body of mass $1kg$ is thrown upwards with a velocity $20m{s}^{-1}$. It momentarily comes to rest after attaining a height of $18m$. How much energy is lost due to air friction ($g=10m{s}^{-2}$)

• A. $20J$
• B. $30J$
• C. $40J$
• D. $10J$

Answer 1

The correct option is A

$20J$

Step 1. Given data

Mass of the body $m=1kg$

Velocity of the body, $v=20m{s}^{-1}$

Height, $h=18m$

acceleration due to gravity, $g=10m{s}^{-2}$

Step 2. Finding the loss in energy, $E$

The energy lost due to the air friction will be equal to the difference in the kinetic energy $K.E.$ and the potential energy $P.E.$

Therefore, the energy lost,

$E=K.E.-P.E.$

$E=\frac{1}{2}m{v}^2-mgh$

$E=\frac{1}{2}\times 1\times 20\times 20-1\times 10\times 18$

$E=20J$

Hence, the correct option is $\left(A\right)$.