Sound intensity is inversely proportional to the square of the distance between the source and the receiver.
That is
I = k/r^2
where
k = constant
r = radius
When r=1, the intensity is I₁ = k/1 = k
When r=3, the intensity I₂ = k/3² = k/9
Therefore
I₂ = I₁ /9
In decibels,
I = 10 log₁₀(I/I₀)
where I₀ = reference intensity
When r=1,
10 log₁₀ (I₁/I₀) = 270
When r =3,
10 log₁₀ (I₂/I₀) = 10 log₁₀ [(I₂/I₁)*(I₁/I₀)]
= 10 log₁₀ [(1/9)*(I₁/I₀)]
= 10 log₁₀(1/9) + 270
= 260.5
Answer: 260.5 dB (nearest tenth)
Answer: 4.9 x 10-3 N
Explanation:
A = 500cm^2 = 5 x 10^-2 m^2
V = 5 m/s
R = 10^-3 g/cm^2.sec = 10^-2kg/m^2 . sec
Prain water = R / V = 10^-2 / 5 = 2 x 10-3 kg/m^3
For the stationary bowl,
dm/dt =pAv= RA
F= dp/dt = (dm/dt) v = RAv = 2.5 x 10^-3 N
Bowl moving upwards to speed u = 2 m/s
dm/dt = pA ( v + u) / v
F = dp/dt = (dm/dt)(v+u) = RA (v+u)^2 / v = 4.9 x 10^-3 N
Answer:
A mirror that has a reflecting surface that is recessed inward is called concave mirror
