Question

A balloon of weight w is falling vertically downwards with a constant acceleration a(< g). The magnitude of the air resistance is

• A. $w$
• B. $w\frac{a}{g}$
• C. $w(1-\frac{a}{g})$
• D. $w(1+\frac{a}{g})$

Answer 1

The correct option is C $w(1-\frac{a}{g})$

Suppose air resistance is F (upwards),
Then from equation for motion of balloon, we have
$w-F=m\times a=\frac{w}{g}.a$
$\therefore F=w(1-\frac{a}{g})$.