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 June 15th, 2019, 11:47 PM #1 Senior Member   Joined: Aug 2014 From: India Posts: 420 Thanks: 1 Find the moment of inertia of the system about the z-axis. A mass of 1 kg is placed at (1m,2m,0). Another mass of 2kg is placed at (3m,4m,0). Find the moment of inertia of the system about the z-axis.
June 16th, 2019, 06:13 AM   #2
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Quote:
 A mass of 1 kg is placed at (1m,2m,0). Another mass of 2kg is placed at (3m,4m,0). Find the moment of inertia of the system about the z-axis.
for a set of $n$ fixed point masses, $\displaystyle I = \sum_{i=1}^n m_i \cdot r_i^2$

in this case ...

$\displaystyle I = \sum_{i=1}^2 m_1 (x^2+y^2)$

 June 16th, 2019, 11:57 PM #3 Senior Member   Joined: Aug 2014 From: India Posts: 420 Thanks: 1 What values of $\displaystyle x$ and $\displaystyle y$ should I substitute in $\displaystyle (x^2+y^2)$?
June 17th, 2019, 05:32 AM   #4
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 Originally Posted by Ganesh Ujwal What values of $\displaystyle x$ and $\displaystyle y$ should I substitute in $\displaystyle (x^2+y^2)$?
Quote:
 A mass of 1 kg is placed at (1m,2m,0). Another mass of 2kg is placed at (3m,4m,0).
$\displaystyle \sum_{i=1}^2 m_i(x_i^2+y_i^2) = (1 \, kg)[(1 \, m)^2 + (2 \, m)^2] + (2 \, kg)[(3 \, m)^2 + (4 \, m)^2]$

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