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# help - astro work watch

1. http://filestore.aqa.org.uk/subjects...R-QP-JUN15.PDF

last on here i somewhat struggle with the units with this

1.6 x 10-2 Mpc s km-1

how do you get this after doing 1/kms^-1Mpcs^-1?
2. (Original post by liverpool2044)
http://filestore.aqa.org.uk/subjects...R-QP-JUN15.PDF

last on here i somewhat struggle with the units with this

1.6 x 10-2 Mpc s km-1

how do you get this after doing 1/kms^-1Mpcs^-1?
question says NGC3842 is 3.3x108 light years distant and receding at 6.3x106 ms-1... estimate the age of the universe in seconds.

since it's asking for seconds it'd be handy to convert everything to SI units... and the AQA data book has the conversion for light years to meters. (at least the one I've got does - but in any case it wouldn't be too hard to work it out from c)
1 light year = 9.46x1015m
so 3.3 light years = ???

you end up with a quantity in the unit of meters per second per meter, that unit can be simplified...

probably the method/explanation are in your notes about estimating the age of the universe from Hubble's constant... but here you're using some empirical data rather than the book value of H0

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