Question

Easy concept yet confused.
In July of 1994, about 20 fragments of comet Shoemaker Levy struck the planet Jupiter, each traveling at a final speed of roughly 60 km/s. These impacts were closely studied yet no one knew exactly how cataclysmic they were because the fragments' sizes (and thus masses) were too small to measure. One estimate of the total energy released by fragment G's impact was 4x10^22 J. Use this to estimate fragment G's size, first assuming that it was a solid rock and then that it was solid ice, which have densities of about 3000kg/m^3 and 920 kg/m^3 respectively.

Answer 1

Are you clear what kind of energy the fragment has ?

Answer 2

Yes, I believe that the object has kinetic energy, and all of its kinetic energy before the collision is then released at impact. so the kinetic energy before impact equals the 4x10^22 J after. Correct?

Answer 3

yes, that's the idea

Answer 4

i set up the equation to look like this:
0.5(20 m) (60,000)^2= 4x10^22. is that the right idea?

Answer 5

yes you've got it right, but I don't think you need that 20 in there, the question gives you the energy associated with the particular fragment 'G'

Answer 6

However, when I do this I get a very large mass and volume for G. for solid rock, it get a volume of 7407407407 m^3

Answer 7

so it was a big piece of rock - have some faith in your work : )

Answer 8

I converted the volumes into the radius of an equivalent sphere, to get more of an idea of the sizes involved

Answer 9

you know the formula for the volume of a sphere in terms of it's radius ?

Answer 10

I found the same figure for the volume of rock that you have, then working back from the volume to the radius of a sphere of the same volume, I got roughly 1.2 km - a big chunk.
Of course, it's even bigger for the case of ice.

Answer 11

Then how come in the directions for the problem it states that the fragments' sizes and thus masses were too small to measure? so shouldn't that result in a smaller answer

Answer 12

Well we're stuck on earth and the fragments were in the vicinity of jupiter, that's an awfully long way away. I guess our powers of observation were not fine enough to accurately detemne the size of bits of rock at that distance.
You need to think of 'large' and 'small' on the scale of the solar system. 1.2km across is pretty small compared to the separation between earth and jupiter

Answer 13

Have you ever looked through a telescope ?

Answer 14

No, but that makes sense now. I even looked up the size of the comet on the Internet and we are pretty close. Thanks for the help, I appreciate it

Answer 15

you're welcome