Question

An object of mass $5kg$ falls from rest through a vertical distance of $20m$ and reaches a velocity of $10m/s$. How much work is done by the push of the air on the object?

• A. $-740J$
• B. $-750J$
• C. $-760J$
• D. $-770J$

Answer 1

The correct option is B $-750J$

From work energy theorem,

work done by weight + work done by air$=\Delta KE$ (change in Kinetic Energy)

$W_{air}=\Delta KE-W_{\left(weight\right)}$

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

$=\frac{1}{2}\times 5\times {\left(10\right)}^2-5\times 10\times 20$

$=-750J$