Understanding Angular Momentum & Energy in Rotational Motion

In summary, a man is rotating with masses in his extended arms. When he pulls his hands towards his stomach, there is an increase in angular velocity and a change in kinetic energy, which is explained by the law of conservation of angular momentum. The work done in this case is equal to the change in kinetic energy, and the force responsible for this work is the force with which the man pulls his hands towards his body. This action also results in a decrease in the man's moment of inertia.
  • #1
Ali Asadullah
99
0
Suppose a man is holding his arms extended in with some masses in each hand. He is set rotating about a vertical axis . If he pulls his hands toward his stomach then according to law of conservation of angular momentum there is an increase in his angular velocity. Also there is a change in his KE from where the energy comes or go? Also We have work=Change in KE
which force does work in dis case?
 
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  • #2
Actually this is question in University Physics H D Young 10 edition Example 10-13.
 
  • #3
What force do you think does work in this case? Where do you think the energy comes from?
 
  • #4
Dear i don't know that is why iam asking from u people.
 
  • #5
Ali Asadullah said:
Dear i don't know that is why iam asking from u people.

How would he decrease his moment of inertia in this case?
 
  • #6
Dear moment ov inertia is mr^2, when he pulls his hands towards his stomach r^2 decreases and hence Moment ov inertia decreases.
 
  • #7
I have asked ma Physics teacher and he replied that the force with which he pulls his hands towards his body actully does work.
Soory for any Grammatical mistake as English is not ma mother tongue.
 
  • #8
Ali Asadullah said:
I have asked ma Physics teacher and he replied that the force with which he pulls his hands towards his body actully does work.
Absolutely.
 

FAQ: Understanding Angular Momentum & Energy in Rotational Motion

What is angular momentum and how is it different from linear momentum?

Angular momentum is a measure of the amount of rotational motion an object has. It is different from linear momentum, which measures the amount of linear motion an object has. Angular momentum takes into account both an object's mass and its rotational velocity, while linear momentum only considers mass and linear velocity.

How is angular momentum conserved in rotational motion?

According to the law of conservation of angular momentum, the total angular momentum of a system remains constant unless acted upon by an external torque. This means that as the rotational velocity of an object increases, its moment of inertia (a measure of its resistance to rotation) will decrease, and vice versa, in order to keep the angular momentum constant.

What is the relationship between angular momentum and rotational inertia?

Angular momentum and rotational inertia are directly proportional to each other. This means that as an object's moment of inertia increases, its angular momentum also increases. This is because a larger moment of inertia requires more force to produce the same amount of angular acceleration, resulting in a greater angular momentum.

How does energy play a role in rotational motion?

In rotational motion, energy is conserved just like angular momentum. However, there are two types of energy involved: kinetic energy and potential energy. Kinetic energy is the energy an object has due to its motion, while potential energy is the energy an object has due to its position. In rotational motion, kinetic energy is mainly affected by an object's moment of inertia and angular velocity, while potential energy is mainly affected by an object's position.

What is the parallel axis theorem and how does it relate to rotational motion?

The parallel axis theorem states that the moment of inertia of an object about an axis parallel to the object's center of mass is equal to the moment of inertia of the object about its center of mass plus the product of the object's mass and the square of the distance between the two axes. This theorem is important in rotational motion because it allows us to calculate the moment of inertia of an object about any axis, not just its center of mass. This is useful in understanding the distribution of mass in an object and how it affects its rotational motion.

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