# Thread: Radius of cylinder

1. ## Radius of cylinder

The radius of a cylinder is quadrupled, determine the percent the volume increase.
Let the height twice as large as the radius.
Assume that the cylinder grows without changing shape.
V=pi*r^2 *h

So this is my task. Normally we get a % the radius increase, and no info about the height, so im kinda stuck.
Dont know if i can use the same method, and i dont know how many % quadrupled would be xD haha, i prolly should.

2. ## Re: Radius of cylinder

If a 3D solid has all of its linear measures increase by a factor $\displaystyle k$, then the volume increases by the factor $\displaystyle k^3$.

3. ## Re: Radius of cylinder

Originally Posted by Mimmi
The radius of a cylinder is quadrupled, determine the percent the volume increase.
If you quadruple the radius only this quadruples the volume

Let the height twice as large as the radius.
Now this becomes a different question!

Assume that the cylinder grows without changing shape.
V=pi*r^2 *h
h= 2r so V= pi* r^2*(2r)= 2pi*r^3

Replacing r with 4r (quadupeling r) gives 2pi*(4r)^3= 4^3(2pi*r^3), which is 4^3= 64 times as large as the value before quadrupling.

[quorte]So this is my task. Normally we get a % the radius increase, and no info about the height[/quote]
Yes, you do. You are told the height is twice the radius.

, so im kinda stuck.
Dont know if i can use the same method, and i dont know how many % quadrupled would be xD haha, i prolly should.

ty!