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NEET 1990 (AIPMT) · Kepler's Laws & Planetary Motion

Kepler's Laws & Planetary Motion question from NEET 1990 (AIPMT)

Q32NEET 1990 · AIPMTMedium

Kepler's Laws & Planetary Motion

A planet is moving in an elliptical orbit around the sun. If $T$ , $V$ , $E$ and $L$ stand respectively for its kinetic energy, gravitational potential energy, total energy and magnitude of angular momentum about the centre of force, which of the following is correct?

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Answer: (c)

(a) Speed changes along the ellipse, so $T$ is not conserved.
(b) $V = -\frac{GMm}{r}$ is always negative.
(c) A bound orbit has total energy $E < 0$ always.
(d) Central force gives zero torque, so both magnitude and direction of $\vec{L}$ are constant.
So the answer is (c) $E$ is always negative.

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