What is the correct moment of inertia for part a using I=m*r^2?

In summary, the conversation discusses using equations to find the moment of inertia and kinetic energy of a uniform disk. Part A uses the equation I=m*r^2 to calculate the moment of inertia, while part B uses the equation K=1/2Iw^2 but has an incorrect moment of inertia. The correct moment of inertia is found using the equation 1/2MR^2, which results in 20.18 kg*m^2. The units for ω, the rotation rate, are rev/s and it needs to be converted to rad/s to be used in the formula for kinetic energy. The conversation concludes with the clarification that the units should be in rad/s, not rev/s.
  • #1
Sneakatone
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for part a I used the equation I=m*r^2 ---> 120(58/100)^2=40.36 kg*m^2

b)I know how to do this using the equation K=1/2Iw^2 but my moment of inertia is incorrect.
 

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  • #2
Sneakatone said:
for part a I used the equation I=m*r^2 ---> 120(58/100)^2=40.36 kg*m^2

b)I know how to do this using the equation K=1/2Iw^2 but my moment of inertia is incorrect.
What is the moment of inertia of a uniform disk of mass, M, and radius, R ?
 
  • #3
I used the equation 1/2MR^2 and got =20.18.
when I plugged everything into the KE equation I had 305.22 J but that is incorrect.
 
  • #4
Sneakatone said:
I used the equation 1/2MR^2 and got =20.18.
when I plugged everything into the KE equation I had 305.22 J but that is incorrect.

What are the units for ω ?
 
  • #5
rev/s
 
  • #6
Sneakatone said:
rev/s

The rotation rate is given you in rev/s, but what units does it need to be into plug it into the formula for KE?
 
  • #7
should it be rev/min or rad/s?
 
  • #8
I got it now it should be in rad/s for some reason I thought It was suppose to be rev/s.
Thank you all!
 

FAQ: What is the correct moment of inertia for part a using I=m*r^2?

What is moment of inertia?

Moment of inertia is a physical property of an object that measures its resistance to changes in rotational motion. It is also known as rotational inertia.

Why is it important to find the moment of inertia?

Knowing the moment of inertia of an object is crucial in understanding its behavior and dynamics when it is rotating. It is used in many fields of science and engineering, such as in designing machines, analyzing the motion of celestial bodies, and developing sports equipment.

How is moment of inertia calculated?

The moment of inertia of an object depends on its mass distribution and the axis of rotation. There are different formulas for calculating moment of inertia for different shapes, such as discs, cylinders, and spheres. The general formula is I = ∫r^2 dm, where r is the distance from the axis of rotation and dm is the infinitesimal mass element.

What factors affect the moment of inertia of an object?

The moment of inertia of an object is affected by its mass and how that mass is distributed around the axis of rotation. In general, the further the mass is from the axis of rotation, the higher the moment of inertia will be. The shape and size of the object also play a role in determining its moment of inertia.

How can moment of inertia be applied in real life?

Moment of inertia has many practical applications in everyday life. For example, it is used in designing cars and bicycles to optimize their performance and stability. It is also important in sports, as athletes and coaches use it to understand and improve movements and techniques. In addition, moment of inertia is crucial in understanding the motion and dynamics of rotating objects in space, such as planets and satellites.

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