Mass center of composite bodies
A composite body is made of joining two or more bodies. Find mass center of the following composite body made by joining a uniform disk of radius r and a uniform square plate of the same mass per unit area.

Explanation

To find the center of mass of a composite body made by joining a uniform disk and a uniform square plate with the same mass per unit area, we can follow these steps:

### Step 1: Define the Mass per Unit Area
Let the mass per unit area be denoted as \( \sigma \).

### Step 2: Calculate the Mass of Each Shape
1. **Mass of the Disk**:
- The area of the disk is given by \( A_d = \pi r^2 \).
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