In planetary motion the areal velocity of position vector of a planet depends on angular velocity $\omega$…

In planetary motion the areal velocity of position vector of a planet depends on angular velocity $\omega$ and the distance of the planet from sun $r$. The correct relation for areal velocity is
  1. $\frac{d A}{d t} \propto \omega r$
  2. $\frac{d A}{d t} \propto \omega^2 r$
  3. $\frac{d A}{d t} \propto \omega r^2$
  4. $\frac{d A}{d t} \propto \sqrt{\omega r}$

Solution

Areal velocity $\frac{d A}{d t}$ depends on angular velocity $(\omega)$ and distance of the planet from sun. $\frac{d A}{d t} \propto w^a r^b \Rightarrow \frac{d A}{d t}=K \omega^a r^b$ Writing the dimensional formula on both sides, $\left[\mathrm{L}^2 \mathrm{~T}^{-1}\right]=k\left[\mathrm{~T}^{-1}\right]^a[\mathrm{~L}]^b$ On comparing, $-a=-1 \Rightarrow a=1$ $b=2$ $\therefore \quad \frac{d A}{d t} \propto \omega r^2$

Asked in: AP EAMCET 2003

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