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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 \((r)\). If so the correct relation for areal velocity is (a) \(\frac{d A}{d t} \propto \omega r\) (b) \(\frac{d A}{d t} \propto \omega^{2} r\) (c) \(\frac{d A}{d t} \propto \omega r^{2}\) (d) \(\frac{d A}{d t} \propto \sqrt{\omega r}\)

Short Answer

Expert verified
The correct relation for areal velocity is \(dA/dt \propto ω r^{2}\).

Step by step solution

01

Identify the basic concept

Areal velocity in the context of planetary motion is given by the area swept out per unit time by the line joining the planet to the sun. Considering a small time duration \(dt\), the planet moves a small distance \(ds\) along its elliptical path, making a very small angle \(d\theta\) at sun. The corresponding small area swept is thus given by \(dA = 0.5 * r * r * d\theta\). The rate of change of area with respect to time, \(dA/dt\), is called the areal velocity.
02

Deducing the relation

Substituting \(d\theta\) with \(ωdt\), where \(ω\) is the angular velocity, we get, \(dA = 0.5 * r * r * ω * dt\). On differentiating both sides with respect to time, we obtain the areal velocity, \(dA/dt = 0.5 * r * r * ω\).
03

Comparing with given options

Comparing the deduced relation with the options, we see it matches with option (c), ie, \(dA/dt \propto ω r^{2}\). So, the correct relation for the areal velocity is \(dA/dt = 0.5 * r * r * ω\), which indicates that the areal velocity is directly proportional to \(ω r^{2}\) .

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