In order to calculate the thermal energy, first let's calculate the power, using the formula:
[tex]P=\frac{V^2}{R}[/tex]For a voltage V = 9 Volts and a resistance R = 50 ohms, we have:
[tex]\begin{gathered} P=\frac{9^2}{50} \\ P=\frac{81}{50}=1.62\text{ W} \end{gathered}[/tex]Now, multiplying the power by the time (in seconds), we can find the energy:
[tex]\begin{gathered} E=P\cdot t \\ E=1.62\cdot7.5\cdot60 \\ E=729\text{ J} \end{gathered}[/tex]In scientific notation, we have an energy of 7.3 * 10^2 J, therefore the correct option is the fourth one.
