What Is the Frictional Force Between Block and Table After Bullet Impact?

In summary, a 2 kg block is initially at rest on a long tabletop. A 5g bullet with a speed of 150m/s embeds itself in the block, causing the combined block and bullet to slide 270cm along the table before coming to a stop. To find the speed of the block, momentum conservation can be used. As for finding the frictional force between the block and table, the initial kinetic energy of the bullet can be used to calculate it, or the combined kinetic energy of the bullet and block right after the collision can be used. However, if heat generated during the collision cannot be neglected, this method may not be accurate.
  • #1
poohead
34
0

Homework Statement


2 kg block of wood rests on a long tabletop. A 5g bullet moving horizontally with a speed of 150m/s is shot into the block and sticks into it. The block then slides 270cm along the table and stops
A) find the speed of the block ( answer: 0.374 m/s)
B)*** find the frictional force between block and table ( answer: )


Homework Equations



Ff = mew * Fn
J=p
Ft = mv

The Attempt at a Solution



after trying to find the solution from relevant momentum formulas, i am still completely stumped as to how i would find the frictional force between table and block

much appreciated if you read this over
 
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  • #2
Well, think about what happens. A bullet with a certain kinetic energy comes along and embeds itself in a block. The combined block and bullet slide across the table. Where does that initial kinetic energy go? If you are allowed to neglect the heat produced in the block during the collision, don't you suppose it goes into work to overcome friction as the block slides to a stop? If you are not allowed to neglect the heat generated, then you need the velocity of the block plus bullet right after the collision that gives you the kinetic energy of the pair at the start and then that energy disappears the same way as before. Think work = force times distance. That should get you started with the second part. However...

The first part makes use of momentum conservation. It would be a useful exercise for you to calculate the answer to the second part both ways (from the KE of the bullet and from the KE of the bullet plus block right after collision.) Do you find a difference?
 

FAQ: What Is the Frictional Force Between Block and Table After Bullet Impact?

1. What is the relationship between wood and bullet friction?

Wood and bullet friction is a measure of the resistance between the surface of the wood and the bullet as they come into contact with each other. This friction depends on factors such as the type of wood, the shape and material of the bullet, and the velocity at which the bullet is traveling.

2. How does the type of wood affect bullet friction?

The type of wood can greatly impact the amount of friction between wood and a bullet. For example, soft woods like pine or cedar have lower friction compared to harder woods like oak or maple. This is because the soft woods have a smoother surface and are less likely to create resistance against the bullet.

3. Is there a difference in bullet friction between freshly cut and aged wood?

Yes, there is a difference in bullet friction between freshly cut and aged wood. Freshly cut wood has a higher moisture content and is softer, which can result in higher friction compared to aged wood that has had time to dry out and become harder.

4. Can the shape and material of the bullet affect wood and bullet friction?

Yes, the shape and material of the bullet can greatly impact the amount of friction experienced when in contact with wood. A pointed or tapered bullet will have less surface area in contact with the wood, resulting in lower friction compared to a flat or round bullet. Additionally, the material of the bullet can also affect friction, with materials like copper or lead having different levels of friction compared to steel or plastic.

5. How does the velocity of the bullet affect wood and bullet friction?

The velocity at which the bullet is traveling can also affect the amount of friction experienced with wood. Higher velocities can result in more friction due to the increased force and impact of the bullet against the wood surface. This can also cause more damage to the wood, resulting in higher levels of friction compared to lower velocities.

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