Question

A hotplate uses 1200 W for 15 minutes. How much energy does it use?The efficiency of real-world systems is always between 0% and 100%.

Answer 1

The value of the power given is,

`P=1200\text{ W}`

The hotplate is used for the time t is,

`\begin{gathered} t=15\text{ minutes} \\ t=15*60 \\ t=900\text{ s} \end{gathered}`

Thus, the energy used is,

`\begin{gathered} E=P* t \\ E=1200*900 \\ E=1080*10^3\text{ J} \\ E=1080\text{ kJ} \end{gathered}`

Hence, the energy used is 1080 kJ.