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Q7.8: NCERT Physics - Part 1 GRAVITATION 7.8 Solution: A comet orbits the Sun in a highly elliptical orbit. Does the…
⚠️ Common Exam Traps & Conceptual Pitfalls
Students often incorrectly assume that because the total mechanical energy is conserved, the kinetic and potential energies must also remain constant. You must recognize that while the sum $K + U$ is fixed, the individual terms vary inversely as the comet moves between perihelion and aphelion.
A comet orbits the Sun in a highly elliptical orbit. Does the comet have a constant (a) linear speed, (b) angular speed, (c) angular momentum, (d) kinetic energy, (e) potential energy, (f) total energy throughout its orbit? Neglect any mass loss of the comet when it comes very close to the Sun.
Step-by-Step Verified Solution
**Answer:** (a) No (b) No (c) Yes (d) No (e) No (f) Yes
**Step-by-Step Explanation:**
(a) Linear speed varies (largest at perihelion, smallest at aphelion) due to conservation of angular momentum.
(b) Angular speed varies for the same reason.
(c) Angular momentum is conserved because gravity is a central force (zero torque about the Sun).
(d) Kinetic energy varies because speed varies.
(e) Potential energy varies because changes.
(f) Total mechanical energy is conserved because gravity is a conservative force [citation:10][citation:15].
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