# Angular momentum Homework Problem

In summary, the conversation is discussing two physics problems - one about finding the angular momentum of a rotating cylinder and the other about determining the acceleration of two masses connected by a cord on a pulley. The participants are trying to figure out the correct equations and values to solve the problems, with one person asking for suggestions on what they may be doing wrong. They also briefly mention another physics problem involving a pulley and ask for ideas on how to solve it.
This is a problem I'm having a world of problem with:

A. What is the angular momentum of a 2.56 kg uniform cylindrical grinding wheel of radius 17.5 cm when rotating at 1480 rpm?

Correct: 6.08 kg*m^2/s

B. How much torque is required to stop it in 6.50 s?

So after 5 tries, I get that Torque = Moment of Inertia * Alpha.

Alpha = Delta (w)/ Delta (t)
Then I = 1/2*m*r^2
and I get .9347 N*m, but the computer does not. Any suggestions as to what I am doing wrong?

Last edited by a moderator:
U've given it 4 sign.digits cf.3 before...

If A is correct (manipulating units),then B is correct,as well.I don't c what it could be.

Daniel.

Well I have lot of these homework questions. Heres another one that I can't figure out.

An Atwood machine consists of two masses, m1 = 6.80 kg and m2 = 8.55 kg, connected by a cord that passes over a pulley free to rotate about a fixed axis

Then there's a picture but I don't know how to link to it. Its just 2 weights on the end of a string around a pully.

The pulley is a solid cylinder of radius R0 = 0.535 m and mass 0.771 kg. Determine the acceleration a of both masses. Ignore friction in the pulley bearing.

10. [1pt]
What percentage error in a would be made if the moment of inertia of the pulley were ignored? Do not enter units.

Any ideas on there either? I did the same kinda thing and said T = F*R=I*Alpha etc etc

## 1. What is angular momentum?

Angular momentum is a measure of the amount of rotational motion an object possesses. It is a vector quantity, meaning it has both magnitude and direction, and is calculated by multiplying the moment of inertia (a measure of an object's resistance to change in rotational motion) by the angular velocity (the rate at which the object is rotating). In simpler terms, it is the quantity of how fast an object is spinning and how difficult it is to stop that spin.

## 2. How is angular momentum conserved?

Angular momentum is conserved in a system when there is no external torque acting on it. This means that the total angular momentum of a system remains constant, even if individual components within the system are experiencing changes in their angular momentum. This conservation law is a fundamental principle in physics and has many important applications, including in the understanding of the motion of planets and stars.

## 3. How is angular momentum related to linear momentum?

Angular momentum and linear momentum are related through a concept known as rotational inertia. Rotational inertia is the tendency of an object to resist changes in its rotational motion, just as mass is the tendency of an object to resist changes in its linear motion. Therefore, the more rotational inertia an object has, the more angular momentum it will have for a given angular velocity.

## 4. What is the difference between angular momentum and torque?

Angular momentum and torque are both related to rotational motion, but they are distinct concepts. Angular momentum is a measure of an object's rotational motion, while torque is a measure of the force that causes an object to rotate. In other words, torque is the force that produces a change in an object's angular momentum.

## 5. How is angular momentum used in real-world applications?

Angular momentum has many practical applications in areas such as engineering, physics, and astronomy. It is used in the design of machines and vehicles that involve rotational motion, such as engines and turbines. In physics, it is used to understand the behavior of spinning objects, such as tops and gyroscopes. In astronomy, it is used to explain the motion of celestial bodies, such as planets and galaxies.

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