Year 12s: what will be the first way you research your future options? >>

Gravitational field direction HELP!

Hey, so I've been attempting this MCQ which asks to find the gravitational field direction at a given point X

Here is the Q itself: https://imgur.com/Kyvsm2C

From what I know, equipotential are lines that show constant potential in a given gravity field.

If the field was to be radial, then the equipotential lines would be concentric circles around the centre. Where as the concentric circles get bigger, the field tends to get weaker. But this isn't the case because the figure shown in the Q has lines in going in all sorts of directions.

I know that equipotential lines always cuts the field lines perpendicularly but I can't see how they would tell the direction of the field at x.

Does the gravitational potential values given in the Q help to find the direction or not?

I'm really confused about this. Any help would be really appreciated.
Thanks!

Reply 1

username3249896

Equipotential lines are perpendicular to the field lines. The direction of the field is in the direction of decreasing potential.

Reply 2

Yatayyat

Original post by BobbJo

Equipotential lines are perpendicular to the field lines. The direction of the field is in the direction of decreasing potential.

So would it look like this then?

Screenshot 2019-03-24 at 14.46.10.png

Sorry if the image isn't clear. Don't know why the quality is so terrible.

(edited 5 years ago)

Reply 3

username3249896

Original post by Yatayyat

So would it look like this then?

Screenshot 2019-03-24 at 14.46.10.png

Sorry if the image isn't clear. Don't know why the quality is so terrible.

No since the field lines should point in the direction of decreasing potential. Your line points towards increasing potential

Reply 4

Yatayyat

Original post by BobbJo

No since the field lines should point in the direction of decreasing potential. Your line points towards increasing potential

Oh okay. Got mixed up with the negative values. So it must be answer C then?

Reply 5

username3249896

Original post by Yatayyat

Oh okay. Got mixed up with the negative values. So it must be answer C then?

Yes

Reply 6

Yatayyat

Original post by BobbJo

Yes

Thanks a lot! Forgot about the fact that field lines point in the direction of decreasing potential.

Reply 7

jb2510

I think its C

You are right that the direction of the grav field is perpendicular to the equipotentials but if you look as the gravitational potential they get increasingly more negative which means to the right delta V tends to zero and the direction of the field always starts from g=0 at infinity and tends to a more negative value.

Hope that helps