Angular Velocity of Disk After Bullet Impact: Calculation Explanation

In summary: But before worrying about disk + bullet, how would you express the angular momentum of a rotating disk alone?
  • #1
khurram usman
87
0
A disk of radius R and mass M is mounted with its axis vertical.It is inially at rest.A bullet of mass m and velocity v is fired horzentally and tengential to disk .It enters the disc at its perimeter.What angular velocity will be acquired by disk?
1=mv/(m+M)R
2=mv/(2M+m)R
3=Mv/mR
4=2mv/(MR+2mR)
5=(m+2M)v/MR

please explain how u compute the answer
 
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  • #2
Have you considered applying the conservation of angular momentum?

Hint: what is the angular momentum of the bullet around the disc's centre just prior to impact? What is the angular momentum due to the combined rotation of the disc+bullet around the disc's centre after the collision?
 
  • #3
cepheid said:
Have you considered applying the conservation of angular momentum?

Hint: what is the angular momentum of the bullet around the disc's centre just prior to impact? What is the angular momentum due to the combined rotation of the disc+bullet around the disc's centre after the collision?

ok...i see the approach
the angular momentum of bullet at tangent to disk will be mvR
now how to calculate velocity?
 
Last edited by a moderator:
  • #4
khurram usman said:
the angular momentum of bullet at tangent to disk will be mvR
Good.
now how to calculate velocity?
First answer cepheid's second question.
 
  • #5
Doc Al said:
Good.

First answer cepheid's second question.

well as i see it the combined angular momentum after collision will be (m+M)Rv'
correct??
 
  • #6
khurram usman said:
well as i see it the combined angular momentum after collision will be (m+M)Rv'
correct??
No, not quite. How would you express the angular momentum of a rotating disk? How does the presence of the bullet stuck onto the disk change that?
 
  • #7
Doc Al said:
No, not quite. How would you express the angular momentum of a rotating disk? How does the presence of the bullet stuck onto the disk change that?

maybe the bullet changes mass distibution
i am not quite getting it
 
  • #8
khurram usman said:
maybe the bullet changes mass distibution
Sure it does.

But before worrying about disk + bullet, how would you express the angular momentum of a rotating disk alone?
 

FAQ: Angular Velocity of Disk After Bullet Impact: Calculation Explanation

What is Angular Velocity?

Angular velocity is a measure of the rate at which an object rotates or spins around a central axis. It is expressed in units of radians per second (rad/s) or degrees per second (deg/s).

How is Angular Velocity calculated?

Angular velocity is calculated by dividing the change in angle (in radians or degrees) by the change in time. It can also be calculated by multiplying the angular speed (in rad/s or deg/s) by the radius of the object.

3. How does a bullet impact affect the angular velocity of a disk?

When a bullet impacts a disk, it imparts a force on the disk which causes it to rotate. The magnitude and direction of this force, as well as the mass and moment of inertia of the disk, will determine the resulting change in angular velocity.

4. What factors can influence the calculation of angular velocity after a bullet impact?

The mass and velocity of the bullet, the mass and moment of inertia of the disk, the distance between the impact point and the center of the disk, and any external forces acting on the disk (such as friction or air resistance) can all influence the calculation of angular velocity after a bullet impact.

5. How is the angular velocity of a disk after a bullet impact useful?

The angular velocity of a disk after a bullet impact can provide valuable information about the impact force and the properties of the disk. It can also be used to calculate the kinetic energy and momentum of the disk, which can be important in analyzing the damage caused by the impact.

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