Four holes of radius 5 cm are cut from a thin square plate of 20 cm...
Four holes of radius 5cm are cut from a thin square plate of 20cm and mass 1kg. The moment of inertia of the remaining portion about Z-axis is
Options
A15kg−m2
B0.37kg−m2
C0.0017kg−m2
D0.08kg−m2
Correct answer
C. 0.0017kg−m2
Step-by-step solution
Area mass density, \sigma=\frac{M}{16 R^2}\left(\because \text{ Area }=4 R ×4 R=16 R²\right)
Massofeachholem1=σπR2=16R2MπR2=16πM
Distance between centre of plate and centre of hole
x=2(2R)2+(2R)2=222R.<imgsrc="/api/proxy−image?url=https \\
Moment of inertia of one hole at about Z-axis
I_1=21m_1 R²+m_1 x²=325πM R²
Moment of inertia of whole plate about Z-axis,
I=6M(4R)2=38M R²
Required moment of Inertia
I_0=I-4 I_1,=\left[\frac{8}{3}-4\left(\frac{5 \pi}{32}\right)\right]MR2=[38−85π]M R²
Given, R=5cm and M=1kg
So, I0=[38−85π]1×25×10−4=0.0017kg−m2