To solve this problem we will apply the concepts related to the thermal efficiency given in an engine of the Carnot cycle. Here we know that efficiency is given under the equation
[tex]\eta = 1 - \frac{T_2}{T_1}[/tex]
Where,
[tex]T_2 =[/tex] Temperature of Cold Body
[tex]T_1 =[/tex]Temperature of Hot Body
[tex]\eta[/tex]= Efficiency
According to the statement our values are:
[tex]\eta = 0.3[/tex]
[tex]T_2 = 210K[/tex]
Replacing we have that
[tex]0.3 = 1- \frac{210}{T_1}[/tex]
[tex]\frac{210}{T_1} = 0.7[/tex]
[tex]T_1 = \frac{210}{0.7}[/tex]
[tex]T_1 = 300K[/tex]
Therefore the temperature of the heat source is 300K
