A 0.25 kg piece of ice at -30 C is warmed by an electric heater and the following graph of temperature is produced. Assume that there has been no loss of energy to the surroundings.
- Use the info on the graph to determine the power output of the heater
- Explain how long it will take to get the ice to the melting point of 0 C
- Explain how long it will take to melt completely once the ice reaches 0 C
- Create a graph like the one above for when the ice starts melting and then complete it, up to this point
Q = micecicetice
The Attempt at a Solution
First calculating the energy:
Q = mct = 0.25 kg x (2.1 x 103 J) x (-30 C - 10 C) = 10, 500 J
Then the power:
P = Q/t = 10, 500J / 150s = 70 W
Now to to find out how long it takes the ice to get to the melting point:
Q = mct = 0.25 kg x (2.1 x 103J) x (-10 C - 0 C) = 5250 J
t = Q/P = 5250 / 70 = 75s
How long it will take the ice to melt completely once it reaches 0 C:
Q = mLf = 0.25 kg x (3.3 x 105) = 82 500 J
t = Q/P = 82500 / 70 = 1180s approximately
Then, 1180s + 75s = 1255s
This is the approximate time it will take the ice to go from -10 C to 0 C, and then completely melt.
Have I done everything correctly? Any confirmation and/or help is greatly appreciated.