Volume of a Cylinder: Calculate Weight

[Eagle's Wings]

Homework Statement

a hollow cylindrical copper pipe is 1.5m long and has an outside diameter of 35cm and an inside diameter of 2.5 cm how much does it weight?

Homework Equations

ρ = M/V = 8.9E3
w = Mg

The Attempt at a Solution

okay, so I know that I can just solve for M because I already have ρ but how do I find volume? do I just do πr^2h but what do I do with the inner and outer diameters?

 

[Mark44]

Homework Statement

a hollow cylindrical copper pipe is 1.5m long and has an outside diameter of 35cm and an inside diameter of 2.5 cm how much does it weight?

Homework Equations

ρ = M/V = 8.9E3
w = Mg

The Attempt at a Solution

okay, so I know that I can just solve for M because I already have ρ but how do I find volume? do I just do πr^2h but what do I do with the inner and outer diameters?

Are you sure about the dimensions of your cylinder? As you gave them, you have a nearly solid chunk of copper with a narrow hole in the middle.

The "hole" is also a cylinder, so you can find its volume and subtract that from the larger volume.

 

[contrivance]

you have a nearly solid chunk of copper with a narrow hole in the middle.

Assuming that OP meant 3.5cm, and 2.5cm respectively;

Use your equation for the Volume of Cylinder:
$$V = \pi r^2 h$$
So like Mark said - find the volume of the cylinder and subtract the volume of the inner 'cylinder' and then you will have the V to find your weight with. (converting cm to m):

$$V_{outer} = \pi (0.035m)^2 (1.5m)$$
$$V_{inner} = \pi (0.025m)^2 (1.5m)$$
$$V_{outer} - V_{inner} = V_{pipe}$$

(in cubic meters)

Now you can find the Mass.