1.Calculate the average density of the Sun from its radius and mass, use the uni

Question

1.Calculate the average density of the Sun from its radius and mass, use the unit of kg/L to express the density. Note that there are 1000 cm3 in 1 liter (1 L).

2.The residents of Earth typically use a total of about 4.50x1020 Joules of energy every year.  What amount of mass (in units of kg) is this equivalent to?

3.Recall that the luminosity of the human body is about 940W. How much mass are you loosing every year from radiating light? Express your answer in units of kg/year.

4.Assuming a star had enough Hydrogen for 9.98x10^55 total PP-chains, how long could the star shine, if the fusion rate were 2.84x10^38 PP-chains per second? Express your answer in units of billions of years

Explanation / Answer

1.So, look up the radius of the sun and the mass of the sun on the internet somewhere. It should be easy to find. Make sure you have metric units like kilometers or meters, and kilograms or metric tons. In fact, convert your radius into centimeters and your mass into kilograms.It will make things easier later. The sun is roughly spherical, so use the formula for the volume of a sphere V=4/3(pi)r^3. So you should now have the volume of the sun in cubic centimeters. Divide this by 1000 to get the volume in liters. Then just divide the mass in kg by the volume in liters to express the density in kg/L.

2.use
E = m c^2
4.50E20 = m (3.00E8)^2
m = 5000 kg

3.Since they give you E (or the information to calculate E) and E = mc^2, what is stopping you from calculating m?

940 W means 940 Joules every second. Multiply by the number of seconds in a year to get the energy in a year

4.t = Q/R = 9.98E55/2.84E38 = 3.514E17 sec = 11.13 GY

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