?

This question has me stumped. I know I need to get an answer of 27 AU but I don't know how. I started calculating using the tidal force formula but just got lost. Any suggestions please and thank you?

"A planet orbits one component of a binary-star system at a distance of 1 AU.

If both stars have the same mass and their orbit is

circular, estimate the minimum distance between the stars for the tidal force

due to the companion not to exceed a "safe" 0.01 percent of the gravitational

force between the planet and its parent star. "

Hi, I am stuck on this problem. I keep getting an answer that I know is wrong. Please help.

Assuming an energy-generation efficiency (ie., the ratio of energy released

to total mass-energy available) of 10%, calculate how much mass a 10^41W quasar

would consume if it shone for 10 billion years. How many solar-mass stars per

year is this equivalent to?

Any suggestions/help appreciated, thank you.

Hi all. I am having trouble with an assignment question. Here it is: A Gamma-ray burst that lasts 22 seconds is recorded in a particular region of the sky. X-Ray spectroscopy of the fading afterglow shoes the Fe (iron) k-alpha line, known to have a rest energy of 6.4 keV, at 5.8 keV. What is the recessional velocity in km/s? I think I have to use v=HoD (Ho is HUbble Constant) at some point, but I am not sure if I have to do some other calculations before then. Any help appreciated, thank you very much.

Facebook keeps changing it's privacy settings. There used to be an easier way to make one's profile completely private. Here is what I want to accomplish. I don't want to be searchable by anyone outside my friends list, and I don't want friends of any of my fb friends (who aren't on my list) to be able to see me. I don't like the direction Facebook is heading in, but I don't want to delete it at the moment (eventually it may come to that but not right now). Any idea how to do this?

I recently bought a house with lots of property around it, and not a lot of ambient light (thank goodness). I love looking at the night sky, and I want to purchase a telescope. Can anyone recommend a good one, or at least tell me what specs I should look for? Thanks :)