1. Calculate the height that a block of ice at 0°C must be dropped to completely
ID: 1544542 • Letter: 1
Question
1. Calculate the height that a block of ice at 0°C must be dropped to completely melt upon impact. Assume no air resistance and that all the energy goes into melting the ice. (Hint: Equate the joules of gravitational potential energy to the product of the mass of ice and its heat of fusion (in SI units, 335,000 J/kg). g = 9.8 N/kg. Do you see why the answer doesn't depend on mass?)
km
2. A 10 kg iron ball is dropped onto the pavement from a height of 100 m. If half of the heat generated goes into warming the ball, find the temperature increase of the ball. (In SI units the specific heat capacity of iron is 450 J/kg°C. g = 9.8 N/kg) Why is the answer the same for any mass ball?
°C
3. The heat of vaporization of ethyl alcohol is about 200 cal/g. If 1.4 kg of it were allowed to vaporize in a refrigerator, how many grams of ice would be formed from 0°C water?
g
Explanation / Answer
1) L = 335000 J/kg, g = 9.8 N/kg
required energyto melt ice Q = mL
from ocnservation fo energy
mL = mgh
335000 = 9.8*h
h = 34.2 m
2) m = 10 kg, h = 100 m,
U = mgh
Q = mgh/2 =10*100*9.8/2 = 4900 J
Q = mCp*DT
4900 = 10*450*DT
DT = 1.09 oC
3) Q = mL
me*Cpe = m*L
1.4*200*4.184 = m*335000
m = 3.5 g
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