How much thermal energy is put out by the speaker?

Thermal energy = 15 Joules

Explanation:

From the attached figure it is given that a loudspeaker converts electrical energy into the kinetic energy of the speaker.

Electrical energy of the speaker is 100 J. The electrical energy is converted to Sound energy of 80 J, friction energy of 5 J and thermal energy. We have to find the thermal energy is put out by the speaker. According to law of conservation of energy :

EE = SE+ TE+ f

Where

EE is the electrical energy

SE is the sound energy

TE is thermal energy

f is friction

100 J = 80 J+ TE + 5 J

So, TE = 15 J

So, the thermal energy of 15 J is put out of the speaker. Hence, the correct option is (b) " 15 Joules ".