# A Curious question About Ballistic Pendulum Solution

• terryds
In summary, the conversation discusses a video about ballistic pendulum problems and questions why the final energy is only a gravity potential energy. There is also a discussion about rotational kinetic energy and the rotational velocity at the peak of the pendulum's displacement. The speaker is unsure about the velocity at the peak but believes it will be v/r. They also ask about the speed of the pendulum at a maximum displacement of sixty degrees and conclude that the velocity is zero at this point, resulting in zero rotational kinetic energy.
terryds
I've watched a video about ballistic pendulum problems.
The illustration is :

I wonder why the final energy is just a gravity potential energy.
I think there is also a rotational kinetic energy (since it will rotate and oscillate)
Is my thought wrong?

terryds said:
also a rotational kinetic energy
What's the rotational velocity at the "peak" of the pendulum displacement?

Bystander said:
What's the rotational velocity at the "peak" of the pendulum displacement?
I'm not quite sure. But, I think it will be v/r
Am I right ?

In your sketch, where the maximum displacement from the vertical is indicated to be sixty degrees, how fast is the pendulum moving?

terryds
Bystander said:
In your sketch, where the maximum displacement from the vertical is indicated to be sixty degrees, how fast is the pendulum moving?
Do you mean the velocity ?
I think it's 0 m/s since it has reached the amplitude.
I get it now.. Because the velocity is zero, so the rotational kinetic energy is zero !

## 1. What is a ballistic pendulum?

A ballistic pendulum is a device used to measure the velocity of a projectile by using conservation of momentum and energy principles. It consists of a pendulum with a bob suspended by a string, and a target where the projectile hits and gets stuck.

## 2. How does a ballistic pendulum work?

When a projectile is fired into the bob of the pendulum, it transfers its momentum and energy to the pendulum. This causes the pendulum to swing to a certain height, which can be measured. By using the conservation of momentum and energy equations, the initial velocity of the projectile can be calculated.

## 3. What factors can affect the accuracy of a ballistic pendulum?

The accuracy of a ballistic pendulum can be affected by factors such as air resistance, friction, and the angle of the pendulum's swing. These factors can cause the bob to not reach its maximum height, leading to incorrect velocity measurements.

## 4. How is a ballistic pendulum used in real-world applications?

A ballistic pendulum is commonly used in forensics and ballistics testing to determine the velocity of bullets and other projectiles. It is also used in physics experiments to demonstrate conservation of momentum and energy principles.

## 5. Are there any limitations to using a ballistic pendulum?

Yes, there are limitations to using a ballistic pendulum. It can only accurately measure the velocity of projectiles that are relatively small and slow-moving. Additionally, it does not take into account factors such as wind and air resistance, which can affect the velocity of the projectile in real-world scenarios.

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