Sound waves can be ranked by their intensity, i, given in the formula below, where r is the distance from the source of a sound with a power output of p.

p=4πir²

solve the formula for the distance from the source, r.

a:

b:

c:

d:

D: r=1/2 sqrt(P/πI)

Step-by-step explanation:

P=4πIr²

We want to solve the equation for r

First divide each side of the equation by 4πI

P/4πI =4πIr²/4πI

P/4πI =r²

Then we need to take the square root of each side.  Normally we would take the ± square root, but distance cannot be negative.

sqrt(P/4πI)  = sqrt(r²)

sqrt(P/4πI)  = r

Notice that there is a 4 in the denominator.  sqrt(4) = 2

sqrt(P/πI)* 1/sqrt(4)  = r

sqrt(P/πI)* 1/2  = r

1/2 sqrt(P/πI) = r

(B)17

Step-by-step explanation:

The dump truck is 21 feet long, 8 feet wide, and 6 feet tall.

Volume of the dump truck=21 X 8 X 6=1008 cubic feet

Since the dump bin can hold dirt equivalent to 1.2 times its capacity,

Volume of dirt the truck can hold=1.2 X 1008=1209.6 cubic feet

If the truck wants to haul 20,000 cubic feet of dirt.

Minimum number of trips=20000/1209.6=16.53 Trips

We round this up to 17 since there is no half trip.

Therefore, the minimum number of trips needed to haul 20,000 cubic feet of dirt is 17.