Calculating Time to Melt Substance at 80 C

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To calculate the time required to melt the substance at 80 C, first determine the power delivered by the circuit using the formula P = U^2/R, where U is the voltage (60 V) and R is the resistance (40 ohms), resulting in a power of 90 watts. Next, calculate the total energy needed to melt the substance by multiplying its mass (0.2 kg) by the heat of fusion (1.35 x 10^5 J/kg), yielding 27,000 J. Finally, divide the total energy by the power to find the time: 27,000 J / 90 W equals 300 seconds. This means it will take 300 seconds to completely melt the substance once it reaches 80 C. Understanding these calculations is crucial for solving similar problems in thermodynamics.
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a portion of an electirc circuit connected toa 40-ohm resistor is embedded in .2 kg of a solid substance in a calorimeter. The externam portion of the circuit is connected to a 60 V power supply.

At 80 C the substance begins to melt. The heat of fusion of the substance is 1.35*10^5 J/kg. How long after the temperature reaches 80 C will it take to melt all of the substance?

I really don't understand how to find time. I get that there's a way to find heat of fusion, but it's already given to me. help please

i have originally posted this in the advanced physics but no one helped. maybe someone here will.
 
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What is the energy delivered per second to the substance?

Can you find the power of the power supply? (Hint: P=UI and Ohm's Law)
 

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