Conservation of Momentum Law- Recoil Velocity (Question)

• seeindubble12
In summary, the conversation discusses the concept of momentum and its conservation in a system. The initial and final momentum of a rifle and bullet are compared, and the equation (mv) + (mv) = (M + m)(v) is used to solve for the final velocity of the rifle. The correct answer is v= .99, and it is emphasized that this is not the correct way to solve the problem. The correct approach is to set the total initial and final momentum of the system equal to m1v1 + m2v2.
seeindubble12
First time posting, I hope I do this correctly!

I am struggling to grasp this concept. This is my attempt at solving. If I am completely off base, will some explain to me again how it works. Our instructor explained it to us with a very detailed formula which, I must confess, has caused me more than a little anxiety because I am not following! Thanks for the help!

1. Rifle (suspended by strings) - 2kg; fires bullet of 0.01 kg at speed of 200 m/s. What is the recoil velocity of the rifle?

2. (mv) + (mv) = (M + m)(v)

3. (0.01)(200) + 0 = (0.01 +2)(v)
2=2.01(v)
divide both sides by 2.01, and the answer is v= .99

Last edited:
This isn't quite right.

Momentum is conserved. What's the total momentum of the system (rifle + bullet) initially? What's the total momentum of the system after the bullet is fired?

Set that total momentum equal to m1v1 + m2v2.

m/s

Hello! Don't worry, the concept of conservation of momentum can be tricky at first. Let me try to explain it in simpler terms. The law of conservation of momentum states that in a closed system (meaning no external forces acting on it), the total momentum before an event is equal to the total momentum after the event. In the case of a rifle firing a bullet, the system includes both the rifle and the bullet.

To solve for the recoil velocity of the rifle, we can use the equation you provided: (mv) + (mv) = (M + m)(v), where m is the mass of the bullet, v is the velocity of the bullet, M is the mass of the rifle, and v is the recoil velocity of the rifle.

In this problem, we know the mass and velocity of the bullet (0.01 kg and 200 m/s, respectively). We also know the mass of the rifle (2 kg). So, we can plug these values into the equation:

(0.01 kg)(200 m/s) + (0 kg)(0 m/s) = (2 kg + 0.01 kg)(v)

Simplifying, we get:

2 kg*m/s = (2.01 kg)(v)

Now, to solve for v, we divide both sides by 2.01 kg:

v = 2 kg*m/s / 2.01 kg

v = 0.995 m/s

So, the recoil velocity of the rifle would be approximately 0.995 m/s.

I hope this helps! Remember, practice makes perfect in understanding these concepts. Keep at it and don't hesitate to ask for clarification if needed. Good luck!

1. How does the conservation of momentum law apply to recoil velocity?

The conservation of momentum law states that the total momentum of a system remains constant unless acted upon by an external force. In the case of recoil velocity, the momentum of the projectile is equal and opposite to the momentum of the gun, resulting in a recoil velocity for the gun.

2. What is the formula for calculating recoil velocity?

The formula for calculating recoil velocity is v = m1v1 / m2, where m1 is the mass of the projectile, v1 is the velocity of the projectile, and m2 is the mass of the gun. This formula assumes that the gun is initially at rest before firing.

3. How does the mass of the projectile affect recoil velocity?

The mass of the projectile directly affects the recoil velocity. As the mass of the projectile increases, the recoil velocity also increases. This is because the momentum of the projectile is directly proportional to its mass.

4. Is recoil velocity affected by the speed of the projectile?

No, recoil velocity is not affected by the speed of the projectile. The only factors that affect recoil velocity are the mass of the projectile and the mass of the gun, as stated by the conservation of momentum law.

5. Can the conservation of momentum law be applied in real-life scenarios?

Yes, the conservation of momentum law can be applied in various real-life scenarios, including recoil velocity. It is a fundamental principle in physics and is used to explain many phenomena, such as car collisions, rocket propulsion, and more.

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