GRAPHS, FUR1 2005 VCAA 9 MC

The relationship between the intensity of sound, and the distance from the source of the sound, is `I = k/d^2`, where `I` is the intensity of sound measured in watts per square metre (W/m²), `d` is the distance in metres from the source, and `k` is a constant.

The intensity of sound is `20` W/m² at a distance of `50` m from the source.

A graph showing the relationship between intensity of sound and distance from the source is

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`A`

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`I = k/d^2 \ \ \ …\ text{(i)}`

`text(Sub)\ I = 20, d = 50\ text{into (i)}`

`20`	`= k/50^2`
`20`	`= k/2500`
`k`	`= 20 xx 2500`
	`= 50000`
`:.\ I`	`= 50000/d^2`

`text(Eliminate)\ E, D\ text(as graph shows linear)`

`text(relationship.)`

`text(Consider)\ A`

`text(Sub)\ (5, 2000)\ text(into)\ I = 50000/d^2`

`text(LHS)`	`= 2000`
`text(RHS)`	`= 50000/5^2`
	`= 50000/25`
	`= 2000`
`:.\ text(LHS)`	`= text(RHS)`

`text(Similarly)\ B\ text(and)\ C\ text(can be)`

`text(eliminated.)`

`=> A`