# Moment of inertia.

1. Nov 27, 2011

### blackfoal

1. The problem statement, all variables and given/known data
A sheet of plywood 1.81 cm thick is used to make a cabinet door 49.1 cm wide by 76.5 cm tall, with hinges mounted on the vertical edge. A small 181-g handle is mounted 45 cm from the lower hinge at the same height as that hinge. If the density of the plywood is 550 kg/m3, what is the moment of inertia of the door about the hinges? Neglect the contribution of hinge components to the moment of inertia.

2. Relevant equations

3. The attempt at a solution
[((weight)*((tall)^2))+((density*tall*thick)*((wide^3)/3))]

answer is not true according to this formula. help me.

2. Nov 27, 2011

### physicsvalk

You can look at this problem from a bird's eye view, since the vertical axis is of no concern to us. How is the moment of inertia of the door from the hinges to handle related to the distance from the hinge to the handle and the door's mass?

I think you're getting confused here with the door's dimensions. Think less of this and more of the physics behind it. Once you get the physics, you'll understand why they give you the length, height and thickness of the door.

3. Nov 27, 2011

### blackfoal

i didnt understand anything your comment :) do you give a formula? maybe i can understand on the formula.

4. Nov 27, 2011

### physicsvalk

5. Nov 27, 2011

### blackfoal

i looked but i can not solute.

6. Nov 28, 2011

### blackfoal

is there anybody for helping to me.