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IB · D · multiple choice

Fields · Question 4

Fields · Original GioPhysics question with a detailed, mark-by-mark answer guide.

Demand
demanding
Marks
1
Topics
1
Answer
Complete
A satellite in a circular orbit about a planetcircular orbitplanet of mass Msatellite of mass mvr
Figure 2A planet is drawn as a large shaded circle labelled 'planet of mass M'. A dashed circle, concentric with the planet and well outside it, is labelled 'circular orbit'. A small rectangle sitting on the dashed circle, above and to the right of the planet, is labelled 'satellite of mass m'. A short arrow from the satellite, drawn along the tangent to the orbit and labelled v, shows the direction in which it travels. A line runs from the centre of the planet out to the satellite and is labelled r.
multiple choice1 mark

A satellite of mass m is in a circular orbit of radius r around a planet of mass M. What is its total energy?

  1. A

    −GMm/(2r)

  2. B

    −GMm/r

  3. C

    +GMm/(2r)

  4. D

    zero

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Answer overviewCorrect answer: A — −GMm/(2r)
01

Answer and reasoning

1 mark
How to approach it

Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.

  1. 1

    The correct choice is A: −GMm/(2r)

  2. 2

    B is the potential energy alone, forgetting that the satellite also has kinetic energy of +GMm/(2r). The total is negative, which is what makes the orbit bound.

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