Question

An object of mass 5 kg falls from rest through a vertical distance of 10 m and acquires a velocity of $10m{s}^{-1}$, the work done by the push of air on the object is $(g=10m{s}^{-2})$

• A. 750 J
• B. -750 J
• C. 250 J
• D. -250 J

Answer 1

The correct option is B -750 J

$W_{air}=\Delta KE-W\left(weight\right)=1/2m{v}^2-mgh=\frac{1}{2}\times 5\times {10}^2-5\times 10\times 20W_{air}=-750J$