Well, I'll try to write the formula in a way that's not confusing,
but I'm afraid it might be slightly confusing anyway.
When you're working with dB, the basic rule is
A change of 10 dB means either multiplying or dividing by 10 .
Multiply something by 10 ==> it increases by 10 dB.
Divide something by 10 ==> it decreases by 10 dB.
It turns out that another way to write all of this is . . .
An increase of 10 dB ===> multiply the original amount by 10¹
An increase of 20 dB ===> multiply the original amount by 10²
An increase of, say, 7 dB ===> multiply the original amount by 10⁰·⁷
A decrease of 10 dB ===> multiply the original amount by 10⁻¹
A decrease of 30 dB ===> multiply the original amount by 10⁻³
A decrease of, say, 13 dB ===> multiply the original amount by 10⁻¹·³
This question says: The sound increases by 5 dB .
That means the original 'intensity' or 'power' of the sound
is multiplied by
10⁰·⁵ = √10 = about 3.162 (rounded) .
From the choices listed, the closest one is (c).
B. Inertia and gravity must be balanced.
Explanation:
It is given that,
= -40 mi/h, = -40 mi/h
The negative sign indicates that x and y are decreasing.
We have to find 
. Equation for the given variables according to the Pythagoras theorem is as follows.
Now, we will differentiate each side w.r.t 't' as follows.
or, 
So, when x = 4 mi, and y = 3 mi then z = 5 mi.
As,
= 
= 
= 52
Thus, we can conclude that the cars are approaching at a rate of 52 mi/h.
The mass is 10.811 hope this helps
