a2: gravitational fields question :)
I'm a little confused regarding this question.
A spacecraft on a journey from the Earth to the Moon feels no resultant gravitational pull from the Earth and the Moon when it has travelled to a point 0.9 of the distance between their centres. Calculate the mass of the Moon, using the value for the mass of the Earth as 6x1024kg.
I understand that the gravitational fields are equal and opposite so they cancel out so you can equate gearth = gmoon.
So
GMmoon/R2 = GMearth/R2
The mark scheme says:
Mearth = 81 Mmoon
Mmoon = (6x1024kg / 81)
Mmoon = 7.4x1022
But if you're equating GMmoon/R2 = GMearth/R2, G cancels and surely R2 would also cancel as you're dividing by 0.92 on both sides?
Hope this made sense.
Thank you.
A spacecraft on a journey from the Earth to the Moon feels no resultant gravitational pull from the Earth and the Moon when it has travelled to a point 0.9 of the distance between their centres. Calculate the mass of the Moon, using the value for the mass of the Earth as 6x1024kg.
I understand that the gravitational fields are equal and opposite so they cancel out so you can equate gearth = gmoon.
So
GMmoon/R2 = GMearth/R2
The mark scheme says:
Mearth = 81 Mmoon
Mmoon = (6x1024kg / 81)
Mmoon = 7.4x1022
But if you're equating GMmoon/R2 = GMearth/R2, G cancels and surely R2 would also cancel as you're dividing by 0.92 on both sides?
Hope this made sense.
Thank you.
The radii wont cancel because one is the distance from earth to that point and the other from the moon to that point. Different values of r. You get a ratio of these distances
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