1.5 kg of liquid water initially at 10°C is heated to 60°C in a teapot equipped with a 1000 W electric heating element inside. The minimum time it takes to heat the water to the desired temperature is
A)3.5 min
B)7.3 min
C)5.2 min
D)16.0 min
E)11.4 min

Question

Quizplus · Accepted Answer

Solved by EES Software. Solutions can be verified by copying-and-pasting the following lines on a blank EES screen. 
C=4.18 "kJ/kg.K"
m=1.5 "kg"
T1=10 "C"
T2=60 "C"
Q_loss=0 "kJ"
W_e=1 "kJ/s"
"Applying energy balance E_in-E_out=dE_system gives"
(time*60)*W_e-Q_loss = dU_system "time in minutes"
dU_system=m*C*(T2-T1) "kJ"
 
"Some Wrong Solutions with Common Mistakes:"
W1_time*60*W_e-Q_loss = m*C*(T2+T1) "Adding temperatures instead of subtracting"
W2_time*60*W_e-Q_loss = C*(T2-T1) "Not using mass"

15 Kg of Liquid Water Initially at 10°C Is Heated