Question

Kepler?? second law regarding constancy of areal velocity of a planet is a consequence of the law of conservation of

• A. Energy
• B. Angular momentum
• C. Linear momentum
• D. None of these

Answer 1

Answer: (B)

Angular momentum

Answer 2

Areal velocity $\frac{ d A }{ dt }$ & angular momentum $L$ of a planet are related by equation $\frac{ d A }{ dt }=$ $\frac{L}{2 M}$, where $M$ is the mass of planet. Since in planetary motion $\bar{L}$ is constant $\left(\bar{\tau}_{\text {ext. }}=0\right)$, hence $\frac{ d A }{ dt }$ is also constant.