# Homework Help: Need physics website

1. Apr 19, 2005

### joejo

Hi guys...

My teacher for my online course gave me an assignment. But never gave us notes/lessons on the questions asked. I will list a few below and I was wondering if someone could please give me some links where I can find some information that will help me understand how to answer these questions.

Amy pours 1 kg of water at 7.0 ° C into a bowl. Calculate the amount of heat energy needed to bring this water to a boil. The specific heat for water is 4186 J/kg. ° C.

A block made of an unknown substance has a mass of 1.5 kg and a temperature of 15.0 ° C. When 2.6 x 104 J of heat is added to the block, its temperature rises to 90 ° C. Calculate the specific heat capacity to the unknown substance

When 1 kg of water at 1000C is mixed with 10 kg of water at 00C, the equilibrium temperature will be

Calculate the amount of heat energy required to boil 1.0 kg of water at 100 ° C into steam at 100 ° C. The latent heat of vaporization for water is 2.26 x 106 J/kg

An elevator motor lifts the elevator full of passengers to a height of 12 m in 30 s. If the mass of the elevator and passengers is 1000 kg, what is the power developed by the motor
The efficiency of an incandescent light bulb is only 4.0%. Calculate the amount of electric energy that must be input to the bulb in order to get 100 J of light energy from the bulb

2. Apr 19, 2005

### eNathan

3. Apr 19, 2005

### HallsofIvy

Look at the units. "specific heat" is $$\frac{Joules}{Kilograms*degrees C}$$. the problem ask for energy (which is in "Joules"). In order to "cancel" the kg and degrees C in the denominator, you need to multiply that "fraction" by some number of kilograms and some number of degrees. You are given "1 kg of water" and you must raise it from 7 degrees to 100 degrees (in other words raise its temperature by 93 degrees) to bring it to a boil. What do YOU think you should do?

As before: specific heat is [tex]\frac{Joules}{kg*degrees C}. You are given Joules, kg and a rise in temperature from 15 degrees to 90 degrees, an increase of 75 degrees. What do you think you need to do to calculate the specific heat?

I think you MEANT 100 degrees C and 0 degrees C. At 1000C, it wouldn't be water! Since these are both water, you don't need to worry about different "heat capacities". This is really just a "weighted average" problem.

Once again, look at the units: "latent heat of vaporization" is [tex]\frac{Joules}{kilogram}. To "cancel" the kg and get only Joules (heat energy), you will need to multiply by some number of kilograms. How many kilograms are involved here?

"Power" is energy divided by time (work per unit time). If you raise 1000 kg 12 meters, what is the work done? If that is done in 30 s, how much work is done per second?

If the efficiency is 4.0%, then the amount of light put out is only 4% of then energy input: 0.04*energy input= 100J. Solve for the energy input.

4. Apr 19, 2005

### joejo

thanks for your help guys...this is grade 11 physics...its not in our outline...but i dont know why were doing it...

but is there a site...there will help me understand it more...listing all the formulas

5. Apr 21, 2005