A 22 kg solid door is 220 cm tall, 91 cm wide. a) What is the door's moment of inertia for rotation about a vertical axis inside the door, 15 cm from one edge? b) What is the door's moment of inertia for rotation about a vertical axis inside the door, 15 cm from one edge?

Respuesta :

Answer

given,

mass of the solid door = 22 Kg

dimension of door = 220 cm x 91 cm

moment of inertia about the hinge

   [tex]I = \dfrac{1}{3}Mr^2[/tex]

r is the distance from the one edge which is equal to 91 cm or 0.91 m

   [tex]I = \dfrac{1}{3}\times 22 \times 0.91^2[/tex]

   [tex]I = 6.073\ kg m^2[/tex]

Moment of inertia about center for rectangular gate is equal to

   [tex]I_{CM} = \dfrac{1}{12}Mr^2[/tex]

moment of inertia for rotation about a vertical axis inside the door, 15 cm from one edge

   [tex]I = I_{CM} + MR^2[/tex]

   [tex]I = I_{CM} + M(\dfrac{91}{2}- 15)^2[/tex]

   [tex]I = \dfrac{1}{12}Mr^2+ M(0.0930)[/tex]

  [tex]I = \dfrac{1}{12}\times 22 \times 0.91^2+ 22 \times (0.093)[/tex]

  [tex]I = 3.56\ Kg m^2[/tex]

The door's moment of inertia for rotation about a vertical axis inside the door, 15 cm from one edge is; I = 3.5648 kg.m²

We are given;

Mass of door; m = 22 kg

Height of door; h = 220 cm = 2.2 m

Width of door; L = 91 cm = 0.91 m

  • Using parallel axis theorem, moment of inertia for rotation about a vertical axis inside the door, 15 cm from one edge is;

I = (1/12)ML² + M(½L - L')²

Where L' = 15 cm = 0.15 m

Thus;

I = (1/12)(22 × 0.91²) + 22(½*0.91 - 0.15)²

I = 1.5182 + 2.0466

I = 3.5648 kg.m²

  • In conclusion, the door's moment of inertia for rotation about a vertical axis inside the door, 15 cm from one edge is

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