Kinetics of Rigid Bodies: Torque and Acceleration Calculation

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SUMMARY

The discussion focuses on calculating the torque required to accelerate a rotor of an electric motor with a mass of 200 kg and a radius of gyration of 150 mm from rest to 1,500 revolutions per minute (rev/min) in 6 seconds. The moment of inertia (I) is calculated using the formula I = 1/2 (mr²), resulting in I = 2.25 kg·m². The angular acceleration (α) can be determined using kinematic equations of rotational motion, which are essential for solving the problem. The user successfully identifies the necessary equations and concepts to proceed with the calculations.

PREREQUISITES
  • Understanding of moment of inertia (I) and its calculation
  • Familiarity with angular acceleration (α) and rotational kinematics
  • Knowledge of the relationship between linear and angular motion
  • Basic proficiency in physics equations related to torque and rotational dynamics
NEXT STEPS
  • Study the derivation and application of the moment of inertia formula for different shapes
  • Learn about kinematic equations for rotational motion, including angular displacement and velocity
  • Explore the concept of torque and its calculation in various mechanical systems
  • Investigate the relationship between linear acceleration and angular acceleration in rigid body dynamics
USEFUL FOR

Students in physics or engineering, particularly those studying mechanics, as well as professionals involved in mechanical design and analysis of rotating systems.

Rob K
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Homework Statement


The rotor of an electric motor of mass 200 kg has a radius of gyration of 150 mm. Calculate the torque required
to accelerate it from rest to 1,500 rev/min in 6 seconds. Friction resistance may be neglected.

Homework Equations


ƩMO = Iα
I = 1/2 (mr2
I am really really stuck here, I don't know what equations I need to use, if this were a straight line question I would use v = u + at, but it isn't so that is wrong


The Attempt at a Solution


All I have so far is this
I = 1/2 (mr2
I = 0.5 * 200 * 0.152
I = 2.25 kgm2

Really lost. I just need some pointers please.

Kind regards

Rob
 
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In calculating I, the radius of gyration is not the radius of a disk. You can look up the formula for it, which is r = \sqrt{I/m} (and note how it is derived).

You can find the angular acceleration α using the kinematic equations of rotational motion (watch units).
 
Brilliant, those are the words I didn't know to find the equation I couldn't find of variables I couldn't relate.

Found them all.

Thank you
 

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