Physics homework help PLEASE!?!?

I just posted this and someone answered but I have no idea what he is talking about so I'm posting it again. Please give me as much detail as possible.

If someone could please give me the formulas or show me how to do this that would help a lot. I have the conversions down but this is really hard for me.

1. How much heat in joules is needed to raise the temperature of 4.0 L of water from 0鎺矯 to 72.0鎺矯?

2. A quantity of gas in a piston cylinder has a volume of 0.569 m3 and a pressure of 200 Pa. The piston compresses the gas to 0.299 m3 in an isothermal (constant-temperature) process. What is the final pressure of the gas?

3. How much heat in kcal must be added to 0.51 kg of water at room temperature (20鎺矯) to raise its temperature to 41鎺矯?

4. How many kilocalories of heat does the operation of a 1190. W hair dryer produce each second?

Physics homework help PLEASE!?!?

I'm assuming this is a basic physics class, in which case the heat capacity of water, and its density are constant with temperature.

Also, we assume that water is actually slightly higher than 0C, such that it is not ice, but liquid water. Otherwise, you have to get into issues with latent heat (removing heat from water at 0C doesn't make it any colder, you have to remove extra heat to get it to freeze).

This is almost all unit conversions. So if you have those down, you're set!

1. First, what is the heat capacity of water? You might use specific heat capacity, which has units of Joules per kilogram Kelvin (J/(kg*K)), or Joules per kilogram per degree celsius.

That's the amount of heat it takes to raise the temperature of 1 kg of water by 1 degree celsius.

Let's say you have this value, call it cp. But, you have a volume of water in liters, not a mass in kg. To convert, you need the density (rho) of water. Now, as it happens, the kilogram is defined such that it is the amount of mass of 1 liter of water. So, 4 L = 4 kg.

So, you have cp (J/kg/degC) times mass (kg) times degree C.

i.e. cp*4kg*72degC = amount of joules needed to raise 4 L of water by 72 degrees. The specific heat of water is 4186 J/kg/C.

A good reference for you might be

http://hyperphysics.phy-astr.gsu.edu/hba...

for #2, you want to use Boyle's law:

PV = nRT

since n = constant (number of atoms), and temp = constant, and R is just a physical constant, then if volume decreases, P must increase.

i.e. PV = constant

so P0*V0 = P1*V1 where P0 and V0 are initial pressure and volume, and P1 and V1 are final pressure and volume. Rearrange terms to solve for final pressure.

3) This is the same as #1, except your deltaT is 21 degrees (41-20), and your mass is different. First, solve for heat in Joules. Then, convert from joules to kcal.

4) First, you must ask yourself what 1190 Watts means. The units of Watt is Joule per second. So 1190 Watts produces 1190 Joules per second. Then, just convert those joules to kcal.