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# REALLY annoying physics question! F = GMm/r^2 watch

1. In 1994 the comet Shoemaker-Levy approached the planet Jupiter on a collision course. Just before the collision, the comet consisted of at least 17 seperate fragments as shown in the picture.

All the fragments had originally been combined in a single comet with a diameter of 9km. Comets like this are made of ice with trapped dust and gas and have a typical density of 500kgm^-3.

Show that the minimum mass for the original comet which formed Shoemaker Levy was about 2x10^14kg.

The thing that bugs me about this question is that you are given density, but not volume. How am I expected to work out big M?

The near side of the comet was 96000km from the centre of Jupiter. At this near side of the comet, Jupiter's gravitational field strength was 13.7458Nkg^-1. Given that Mass of jupiter = 1.8987 x 10^27 and the gravitational constant G = 6.6720 x 10^-11Nm^2kg^-2, calculate Jupiter's gravitational field strength at the far side of the comet
I don't even know where to start on this one

i know this is sort of a long question, but i've done the revision and just can't seem to answer these questions. my exam is in a months time so i'd be really grateful if anyone can walk me through this! thanks!
2. (Original post by ifailatlife)
In 1994 the comet Shoemaker-Levy approached the planet Jupiter on a collision course. Just before the collision, the comet consisted of at least 17 seperate fragments as shown in the picture.

All the fragments had originally been combined in a single comet with a diameter of 9km. Comets like this are made of ice with trapped dust and gas and have a typical density of 500kgm^-3.

Show that the minimum mass for the original comet which formed Shoemaker Levy was about 2x10^14kg.

The thing that bugs me about this question is that you are given density, but not volume. How am I expected to work out big M?

The near side of the comet was 96000km from the centre of Jupiter. At this near side of the comet, Jupiter's gravitational field strength was 13.7458Nkg^-1. Given that Mass of jupiter = 1.8987 x 10^27 and the gravitational constant G = 6.6720 x 10^-11Nm^2kg^-2, calculate Jupiter's gravitational field strength at the far side of the comet
I don't even know where to start on this one

i know this is sort of a long question, but i've done the revision and just can't seem to answer these questions. my exam is in a months time so i'd be really grateful if anyone can walk me through this! thanks!
1. You are not given the volume but you are told the original comet had a diameter of 9km. Assume the comet was a sphere.
2. Use the formula F=GMm/r2 to find the field strength (force on a mass of 1kg) at a distance equal to the nearside of the comet plus the diameter of the comet to find the value at the far side.

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