This is a job for Newton's 2nd Law! F = ma. We want to know the acceleration, so let's solve it for a, and get a = F/m. Now if we double the force, we'll have a' = 2F/m (where a' is the modified acceleration), and then if we decrease the mass by a half, we'd get a'' = 2F/(1/2*m) = 4F/m. We know the original acceleration was a = F/m, so let's sub that into the a'' equation and get: a'' = 4a, so a'' is 4 times the magnitude of our starting a.
Sound intensity of 1 baby, I = 8*10^-8 W/m^2
The sound heard should be higher by:
10*log (n) where for 5 babies, n = 5. Then
10*log (n) = 10*log (5) ≈ 7 dB
Also give is the reference sound, Io = 1.0*10^-12 W/m^2
Therefore,
Sound intensity, L1 = 10*log (I/I1) = 10*log [(8*10^-8)/(1*10^-12)] ≈ 49 dB
Therefore, total intensity for the five babies is:
Total intensity = 49+7 = 56 dB