Water heater contains 51 gal of water. part a how many kilowatt-hours of energy are necessary to heat the water in the water heater by 25 ∘c?

5.6 kilo-watt hours  
The specific heat of water is 4.1796 J/(K*cm^3) which means that in order to raise the temperature of 1 cubic centimeter of water 1 Kelvin, it takes 4.1796 Joules of energy. So let's start by converting 51 gallons into cubic centimeters: 
51 gal * 3.78541 L/gal * 1000 cm^3/L = 193055.91 cm^3  
Since the size of 1 Kelvin is the same as the size of 1 degree C, we don't need to worry about converting the temperature. 25 degree C increase is the same as a 25 K increase. So let's calculate how many joules we need. 
193055.91 cm^3 * 25 K * 4.1796 J/(K*cm^3) = 20172412.04 J 
20172412.04 J = 20172412.04 kg*m^2/s^2 
 20172412.04 kg*m^2/s^2 / 3600 s/h = 5603.447788 watt hours. 5603 / 1000 = 5.6 kilowatt-hours.

Size

The Sun is 1,390,000 km in diameter. That compares with 12,756 km for diameter of the Earth. In other words, the diameter of the Sun is over 100 times the diameter of the Earth.

In June, 2004, Venus passed in front of the Sun, as seen from the Earth. Since the diameter of Venus is only slightly less than that of Earth (12,104 km)

Mass

The mass of the Sun is about 2 x 1030 kilograms (2 followed by 30 zeros). It is one of the larger stars in our Milky Way galaxy. The median size of stars in our galaxy is less than half the mass of the Sun. In comparison, the Earth is 6 x 1024 kg. This means that the mass of the Sun is over 300,000 times greater than that of the Earth.

other than its Big,Orangish-yellowish, round like a ball, and extremly hot