# Forensic Expert Bullet Velocity-Ballistic Pendulum :uhh:

• samdiah
In summary, a forensic expert fired a 5.50g bullet into a ballistic pendulum with a bob that had a mass of 1.75 kg. The pendulum swung to a height of 12.5 cm before dropping back down, allowing for the calculation of the bullet's velocity just before impact. The formula used was v=sqrt(2gh), resulting in a velocity of 1.565 m/s. The conservation of momentum and energy were taken into consideration, and the final velocity of the bullet was determined to be 499.599 m/s. The question was deemed easy due to its 4 marks.
samdiah
A forensic expert needed to find the velocity of a bullet fired from a gun inorder to predict the trajectory of a bullet. He fired a 5.50g bullet into ballistic pendulum with a bob that had a mass 1.75 kg. The pendulum swung to a height of 12.5 cm above its rest position before dropping back down. What was the velocity of the bullet just before it hit and became embedded in the pendulum bob?

I think I have an understanding of the queation, but just wanted to ensure I am on the right path.

I figured that in the middle kenetic energy E=1/2 mv2 will not be conseved, but momentum is conserved. So if u is the velocity of bullet in start then u=((m+M)v)/m

In the swing to the height of 12.5 cm the potential and kenetic energy will be conserved since both the mass of pendulum and bullet swing up after collision.
so v=sqrt(2gh)

v=sqrt(2*9.8*0.125)
=1.565 m/s

u=((m+M)v)/m
=((5.50+1750)1.565)/5.50
=499.599 m/s

Is this question really this easy because its 4 marks?

samdiah said:
A forensic expert needed to find the velocity of a bullet fired from a gun inorder to predict the trajectory of a bullet. He fired a 5.50g bullet into ballistic pendulum with a bob that had a mass 1.75 kg. The pendulum swung to a height of 12.5 cm above its rest position before dropping back down. What was the velocity of the bullet just before it hit and became embedded in the pendulum bob?

I think I have an understanding of the queation, but just wanted to ensure I am on the right path.

I figured that in the middle kenetic energy E=1/2 mv2 will not be conseved, but momentum is conserved. So if u is the velocity of bullet in start then u=((m+M)v)/m

In the swing to the height of 12.5 cm the potential and kenetic energy will be conserved since both the mass of pendulum and bullet swing up after collision.
so v=sqrt(2gh)

v=sqrt(2*9.8*0.125)
=1.565 m/s

u=((m+M)v)/m
=((5.50+1750)1.565)/5.50
=499.599 m/s

Is this question really this easy because its 4 marks?

Yes it is.

Thanks a lot!

## What is a ballistic pendulum?

A ballistic pendulum is a device used to measure the velocity of a projectile by capturing it in a swinging pendulum and measuring the pendulum's displacement.

## How does a ballistic pendulum work?

A ballistic pendulum works by having the projectile enter the pendulum and become lodged in a target, causing the pendulum to swing. The height of the pendulum's swing is then measured and used to calculate the projectile's velocity.

## What is the purpose of using a ballistic pendulum in forensics?

A ballistic pendulum is used in forensics to determine the velocity and trajectory of a bullet in a crime scene. This information can help recreate the events of a shooting and provide evidence in a court case.

## How accurate is a ballistic pendulum in determining bullet velocity?

The accuracy of a ballistic pendulum in determining bullet velocity depends on various factors such as the condition of the pendulum, the type of ammunition used, and the precision of the measurements taken. However, it is generally considered to be a reliable method with a margin of error of around 5%.

## Are there any limitations or drawbacks to using a ballistic pendulum in forensics?

Yes, there are some limitations to using a ballistic pendulum in forensics. These include the potential for human error in measuring and recording data, the potential for damage to the pendulum from repeated use, and the fact that it can only provide information on the velocity and trajectory of a single shot. It is important to use the results of a ballistic pendulum in conjunction with other forensic evidence to paint a complete picture of a crime scene.

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