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Gravitational Fields Questions

Q7.

(a) State what is represented by gravitational field lines.

Gravitational field lines show the direction (and relative magnitude) of force that would act on a mass placed in the force field.

OR

Gravitational field lines show the direction a mass placed in the force field would initially move.

[1 mark]

(b) The diagram shows the gravitational field above a small horizontal region on the surface of the Earth.

(i) Suggest why the field lines converge over a small area at K.

The lines are closer together at K, this shows that the field is stronger in that area.

This idicates that the material forming the Earth at K has a higher density than the surrounding material.

Saying the ‘force is stronger’ does not gain you the first mark. You have to say the 'field is stronger'.

[2 marks]

(ii) A ball travelling at constant speed passes position J moving towards position K in the diagram above. Assuming friction is negligible, explain any change in the speed of the ball as it approaches K.

I think this is a very poorly worded question.

The question is only about the horizontal speed of the ball and how that changes as it approaches K. Many candidates got sidetracked by thinking about the force making it accelerate vertically - and this does not surprise me!

At J the ball continues at a steady horizontal speed as there is not a horizontal component to the field lines. The ball will speed up/accelerate when moving towards K because the angled field lines between J and K have a horizontal component towards the right ie towards K meaning that the gravitational potential is lower at K

[2 marks]

(Total 5 marks)