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<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>
<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>
<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>

Help with this question please

As a comet orbits the Sun the distance between the comet and the Sun continually
changes. As the comet moves towards the Sun this distance reaches a minimum value.
Which one of the following statements is incorrect as the comet approaches this
minimum distance?
A The potential energy of the comet increases.
B The gravitational force acting on the comet increases.
C The direction of the gravitational force acting on the comet changes.
D The kinetic energy of the comet increases.

To me A and C are incorrect. This is because as the comet approaches the sun, its potential energy decreases and it gains kinetic energy. So I thought A must be wrong. However part C says the direction of gravitational force acting on the comet changes. This must also be wrong because gravitational force is the centripetal force and its always acting towards the centre of the sun, so the direction of the force never changes. So C must be wrong also

The correct answer is that A is incorrect, can anyone explain why C is correct?

Thanks
If the force is always directed towards the sun then as the comet moves around the sun the direction (orientation) of the force changes.
If it points this > way when at one end of its orbit it will point this < way at the other.
That's a change of 180 degree in direction.
ahhh, ok thanks
Reply 3
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Lukeeee
One way to remember it (I believe you're doing AQA as I recognise the question) is that the gravitational force is equal to the centripetal force mv^2/r = GMm/r^2.

If this is true then the fact that a centripetal force is always radial also applies to a gravitational force. :smile:

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