On a good night, the front row of the Twisted Sister concert would surely result in a 120 dB sound level. An IPod produces 100 dB. How many IPods would be needed to produce the same intensity as the front row of the Twisted Sister concert?

100 iPods

Explanation:

The deciBell scale is logarithmic, and thus, it turns multiplying into adding.

Initially, it was the Bell scale, purely logarithmic, where "times 10" is translated into "plus 1" (just like normal logs). However, the steps became too big and so they divided the Bell in 10 parts, the deciBell.

The levels above could well have been called 10B and 12B.

Usually, we define the dB scale for intensity as:

I(dB) = 10•log(I)

Thus,

I = 10^(I(dB)/10)

Now 120 dB gives us units of I = 10^(120/10) = 10^12 Pa (assume the dB are measured to 1 Pa) and 100 dB is 10^10 Pa.

Thus, we would need 100 ipods to get the same intensity

3.2x10^7

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.