Question

A balloon has a mass of $10$ gram in air. The air escapes from the balloon at a uniform rate with a velocity of $5cm/s$ and the balloon shrinks completely in $2.5s$ . The average force acting on the balloon will be

• A. 200 dyne
• B. 20 dyne
• C. 20 newton
• D. 2000 dyne

Answer 1

Answer: (B)

According to Newton's second law of motion,
$F=$ time rate of change of linear momentum
$=\frac{dp}{dt}=\frac{d}{dt}(mv)$
Since, here velocity $(v)$ is constant.
$\Rightarrow F=v\frac{dm}{dt}$
Here, $dm=10g,dt=2.5s$
$\Rightarrow F=\frac{5\times 10}{2.5}=20gcms$
$=20$ dyne