Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A rod of length has a mass per unit length , where is the distance from one end. How far from that end is its centre of mass?
The centre of mass is the mass-weighted average position: , and the same for and . For a continuous body, . A hole can be treated as a negative mass.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. Integrate for the mass and its first moment.
Step 1. Mass. (times ).
Step 2. Moment. .
Step 3. Divide. .
Answer: from the light end.
Check. It is past the middle (), toward the heavy end, as it should be.
Watch out. For a uniform rod the answer would be . Here the mass is not uniform, so the centre shifts.
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