Physics help?

[xcellerate]

1) A 112 g cube of ice at 0°C is dropped into 1.0 kg of water that was originally at 74°C. What is the final temperature of the water after the ice has melted?

specific heat of water = 4186 j/kg*c
specific heat of ice = 2090 j/kg*c
latent heat of fusion for water = 3.33x10^5 j/kg

I got 62.8282*c and the computer says, "Your answer is within 10% of the correct value. This may be due to roundoff error." Yet, still counts it as wrong.

2) What mass of steam that is initially at 120°C is needed to warm 340 g of water and its 300 g aluminum container from 20°C to 50°C?

specific heat of aluminum = 900 j/kg*c
specific heat of steam = 2010 j/kg*c
latent heat of vaporization for water = 2.26*10^6

I got one answer, and the computer says is wrong, and it seems no matter what else i try, and i always get that same answer. These are the last 2 of 15, i always get so close.

 

[dream431ca]

Give us the forumlas for each question.

 

[xcellerate]

...if i had the forumlas i could do it. I can plug in numbers, the problem is i need to figure out what the equations are, and then solve. Basically his class works like this, "f=ma--now what is the escape velocity for a 9,000kg rocket ship if it launches from a 42* angle off venus?"

 

[Dan]

Q (heat transfer) = m (mass) * c (specific heat capacity) * dT (change in temp)

For the first one make sure that you only use the specific heat for water. Toss out the specific heat of ice:
Q = 0.112*3.33E5 + 0.112*4186*T2
Q = 1*4186*(T2 - 74) [taking Q to be heat transferred to the ice]
I don't have a calculator with me, but that's 2 equations two unkowns. Solve for T2

For the 2nd question you need to first make an assumption about wether the final temp is greater than or less than 100. It's probably less than so remember to add the heat of vaporization.

I'm taking Q to be the heat transfered to the water and aluminum

Q = msteam*2010*20 + msteam*2.26E6 + msteam*4186*50
Q = 0.340*4186*30 + 0.300*900*30

same deal, I don't have a calculator