A professor's office door is 0.99 m wide, 2.2 m high, 4.2 cm thick; has a mass of 27 kg, and pivots on frictionless hinges. A "door closer" is attached to door and the top of the door frame. When the door is open and at rest, the door closer exerts a torque of 5.6 N*m. What is the moment of inertia of the door? If you let go of the open door, what is its angular acceleration immediately afterward?

Respuesta :

Answer:

[tex]I=8.8209\ kg.m^2[/tex]

[tex]\alpha=0.6348\ rad.s^{-2}[/tex]

Explanation:

Given:

  • width of door, [tex]w=0.99\ m[/tex]
  • height of the door, [tex]h=2.2\ m[/tex]
  • thickness of the door, [tex]t=4.2\ cm[/tex]
  • mass of the door, [tex]m=27\ kg[/tex]
  • torque on the door, [tex]\tau=5.6\ N.m[/tex]

∵Since the thickness of the door is very less as compared to its other dimensions, therefore we treat it as a rectangular sheet.

  • For a rectangular sheet we have the mass moment of inertia inertia as:

[tex]I=\frac{1}{3} m.w^2[/tex]

[tex]I=\frac{1}{3}\times 27\times 0.99^2[/tex]

[tex]I=8.8209\ kg.m^2[/tex]

We have a relation between mass moment of inertia, torque and angular acceleration as:

[tex]\alpha=\frac{\tau}{I}[/tex]

[tex]\alpha=\frac{5.6}{8.8209}[/tex]

[tex]\alpha=0.6348\ rad.s^{-2}[/tex]

The moment of inertia of the door is [tex]8.8209\ kg.m^2[/tex]

The angular acceleration immediately afterward is [tex]0.6348\ rad.s^{-2}[/tex]

Calculation of moment of inertia & the angular acceleration:

(a) The moment of inertia should be

[tex]= 1\div 3 m.w^2\\\\ = 1\div 3 \times 27 \times 0.99^2\\\\= 8.8209 \ kg.m^2[/tex]

(b) The angular acceleration should be

[tex]= 5.6 \div 8.8209\\\\= 0.6348\ rad.s^{-2}[/tex]

Learn more about the acceleration here: https://brainly.com/question/24815335