Light related questions, answer as many or as few as you feel like doing?

Question

Disclaimer: I'm not trying to cheat or anything, I just need a few of these problems done with work shown and explained to me.

1)What is the length of a light-year in meters?

2)How many years and seconds does it take light to travel from the star Alpha Centauri to Earth? (25.8 trillion miles away)

3)Approximatly 4x10^9 kg of matter is converted to energy in the sun each second. At this rate how long should it take to have all of the suns energy converted to mass? (I don't know what you need to know in terms of what is necessary to complete this problem, but there is a lot of numbers about it on wikipedia ie. volume etc...)

4)How many kms in one parsec? How many light-years

Okay, last one

5) Suppose you have a mass of 70 kg on Earth. How much would you wigh in pounds and Newtons on the surface of a white dwarf star, the same size as Earth, but having a mass 300,000 times that of Earth (nearly the mass of the sun)?

Okay, thats it, I'm going to post this in 2 places.

Dude this is coming off of a study guide that is like 50 questions (5 is like 10% of the problems). If you want to be a jackass fine, but Wikipedia doesn't do the problems it just gives the answer. I want to know the process not just the answers.

Answer 1

1. Since the light year is a specifically defined quantity, no "work" is required.
A light year is 9,460,730,472,580.8 km - I'll let you do the math (multiply by 1000 to get it in meters).

2. Can't get it down to the second, we don't have the distance of A. Cent. down to the meter. 25.8 trillion miles is as close as we can get.
Since a light year is the measurement of the distance light travels in one year, if you know the distance and the velocity, you can calculate the time: t = d/v.

3. To calculate, you just need to know the total mass of the sun. If 4 x10^9 kg is "lost" each second, and you know the total mass, you can calculate the number of seconds it would take. But that would all be just theoretical. Once the sun has fused about 10% of its original mass of hydrogen, it will leave the main sequence and expand to a red giant, then it will eventually shrink to a white dwarf (at this point fusion has ended and the sun only loses its mass due to the solar wind).

4. Approximately 3.086 x 10^13 km (about 3.262 light-years).

5. Gravity is directly proportional to the mass of the 2 objects and inversely proportional to the square of the distance.
In your example, the distance doesn't change, but the mass increases by 300,000. So the gravitational force at the surface is 300,000 times the force on Earth.
A 70 kg weight would weigh 21,000,000 kg (sorry, I don't think in Newtons, but you get the idea).

Answer 2

oh ok. I'm so sorry for trying to protect your grades.

I won't do it again. Good luck

anyway, if gravity is 300,000 time more than earth and you weigh 70 kg on earth, then you need to RE learn multiplication, since you don't notice it in the question.

300,000 X 70kg = your answer
use http://www.worldwidemetric.com/metcal.htm to convert into pounds
and use http://www.onlineconversion.com/force.htm to convert to newtons

thats all the help you'll get from me. I don't want to make your brain weak, by doing the work for you.

Answer 3

its great that i wiki only gives answers or else i would have failed my bio final