Conservation of Momentum with Friction

In summary, a bullet of mass 6.32 g is fired into a block of mass 2.30 kg on a rough surface with a coefficient of friction of 0.28. The bullet becomes stuck in the block and together they slide and come to rest. The equations used are KE=1/2 mv^2 and p=mv. There is missing information needed to solve the problem accurately.
  • #1
derf709
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Homework Statement



A bullet of mass m = 6.32 g is fired into a block of mass M = 2.30 kg that is initially at rest on a rough surface. (The coefficient of friction is 0.28 between the block and the surface.) The bullet ends up stuck in the block, and together they slide across the surface and come to rest.

Homework Equations



KE=1/2 mv^2
p= mv

The Attempt at a Solution



(.00632)(vi)=(.00632+2.30)(Vf)

I was thinking I could set the total kinetic energy minus friction equal to zero, and then solve for the velocity, which could be used in the momentum equation. is this on the right track?

1/2(.00632+2.30)v^2-6.33=0
v=2.34 m/s

Plugging in final velocity, I got an initial velocity of 855 m/s. It sounds plausible, but the answer is incorrect. Any suggestions? :)
 
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  • #2
Your problem is missing information. You can't subtract friction force in Newtons from KE which is in in Newton-meters (joules). You need to know the distance traveled while coming to a stop.
 

FAQ: Conservation of Momentum with Friction

What is conservation of momentum?

Conservation of momentum is a fundamental principle in physics that states that the total momentum of a closed system remains constant. In other words, the total amount of motion in a system does not change unless an external force acts on it.

How does friction affect conservation of momentum?

Friction is a force that acts in the opposite direction of motion and can cause objects to slow down or stop. In a closed system, friction can cause a decrease in the total momentum due to the loss of kinetic energy. This means that the total momentum before and after a collision will not be exactly the same, but it will still be conserved.

Can conservation of momentum be applied to real-world scenarios?

Yes, conservation of momentum is applicable to all physical interactions in the real world. It is a fundamental law of nature and can be used to explain and predict the behavior of objects in motion, including collisions and explosions.

Is there a difference between elastic and inelastic collisions in terms of momentum conservation?

Yes, in an elastic collision, both momentum and kinetic energy are conserved, meaning the total momentum before the collision is equal to the total momentum after the collision. In an inelastic collision, only momentum is conserved, meaning the total momentum before and after the collision may not be equal due to the loss of kinetic energy.

How does the coefficient of friction affect momentum conservation?

The coefficient of friction affects the amount of friction acting on an object, which in turn affects the amount of kinetic energy lost due to friction. The higher the coefficient of friction, the more kinetic energy will be lost, resulting in a greater change in momentum. However, overall momentum will still be conserved.

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