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Question 19M.2.HL.TZ2.9aii

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.HL.TZ2.9aii
Level HL Paper 2 Time zone TZ2
Command term Discuss Question number aii Adapted from N/A
aii.
[Maximum mark: 2]
19M.2.HL.TZ2.9aii

A planet of mass m is in a circular orbit around a star. The gravitational potential due to the star at the position of the planet is V.

(aii)

Suppose the star could contract to half its original radius without any loss of mass. Discuss the effect, if any, this has on the total energy of the planet.

[2]

Markscheme

ALTERNATIVE 1

«at the position of the planet» the potential depends only on the mass of the star /does not depend on the radius of the star ✔

the potential will not change and so the energy will not change ✔

ALTERNATIVE 2

r / distance between the centres of the objects / orbital radius remains unchanged ✔

since  E T o t a l = − 1 2 G M m r , energy will not change ✔

 

Examiners report

A large number of candidates thought that the total energy of the planet would change, mostly double.

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