Question

M is directly proportional to r2.when r=2,m=14.Work out the value of r when m =224

Answer 1

`r=8`

Explanation:

we know that

A relationship between two variables, x, and y, represent a proportional variation if it can be expressed in the form
`y=kx`

In this problem

Let

`y=m`

`x=r^(2)`

substitute

`m=kr^(2)`

Find the value of k

For
`r=2, m=14`

`14=k(2^(2))`

`14=4k`

`k=14/4` ----> constant of proportionality

the equation is equal to

`m=(14/4)r^(2)`

Find the value of r when m=224

substitute in the equation and solve for r

`224=(14/4)r^(2)`

`r^(2)=224*4/14`

`r^(2)=64`

`r=8`