" Don't confuse watts with amps !!
The power rating of speakers is used as a sales point and usually bears
little resemblance to that actually developed, also of course in the average
unit the power developed will vary with the frequency.
You could expect a lower output with a mismatch of the 4ohm speakers.

Okay, This is where I get confused. The car has a 12 volt battery.

1) Does the amp produce 40 amps?
2) Or is it powered by 40 watts?
3) Is the amp limited by the 12 volt battery?

I do not understand the difference between volts and watts/joules? Are
they not the same?

Where and how do volts become watts and vice versa?