An electric kettle. The input energy is 10 Joules. The useful output energy is heat 9

Joules. Wasted energy is sound 1 Joules.

Efficiency = 90 %

Wasted energy = 10 %

Explanation:

Since we have the input energy and useful output energy of the electric kettle, the only thing we are required to calculate here is its efficiency. This is gotten from

E = useful output energy/input energy * 100

E = 9/10 * 100 = 90 %

The percentage of wasted energy is

W = wasted energy/input energy * 100

W = 1/10 * 100

W = 10 %