8.It\'s a cool day, about 10 o C, so you plan to make about 5.0 kg of clear soup

Question

8.It's a cool day, about 10 oC, so you plan to make about 5.0 kg of clear soup using your slow cooking crockpot. To decide whether the soup will be ready for dinner, you estimate how long it will take before the soup gets to its boiling point. Before adding the ingredients, you turn the crockpot over and read that it is a 200-ohm device that operates at 120 volts. Since your soup is mostly water, you assume it has the same thermal properties as water, so its specific heat capacity is 4200 J/(kg oC) and its heat of vaporization is 2.3 x 106 J/kg.

Explanation / Answer

heat required=mCp*(Tf-Ti)=5*4200*90=1.89*10^6J

Power of heater=V^2/R=72W

Time=Energy/power=26250s=7.3 hours

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