Solving for Initial Speed of a 5.5g Bullet Impacting Wood Block

In summary, the conversation is about finding the initial speed of a bullet that has been fired into a block of wood. The wood block is initially at rest on a post and after the collision, both the block and the bullet land 2.5m from the base of the post. The student suggests using the momentum equation and provides step-by-step instructions on how to find the initial speed of the bullet. The conversation also includes a reminder to post homework questions in the appropriate forum and to not give away answers.
  • #1
CoolBlueR
2
0
I need help with this. I don't know what equation to use.

A 5.5g bullet is fired into a block of wood w/a mass of 22.6g. the wood block is initially at rest on a 1.5m tall post. after the collision, the wood block and bullet land 2.5m from the base of the post. how do you find the initial speed of the bullet?

I think that you would use the momentum equation, but I don't understand where the height and displacement come in.
 
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  • #2
I think this is how you would do it:

Find the time it takes the block to hit the floor:

s =ut + 0.5at^2
1.5 = 0.5*9.8t^2
t = 0.55 seconds

Then use this to work out what acceleration would be needed to move the block 2.5m in that time.

2.5 = 0.5a*0.55^2
a = 16.33 m/s

Then work out the velocity of the block when it hits the ground.

v=u+at
v=8.98 m/s

Use this in the momentum forumulas.

m1v1 + m2v2 = momentum after

8.98*0.0281 = 0.25
(final velocity*total mass of both the block and the bullet)

Then work back with the momentum forumula.

0.0055v + 0.0226*0 = 0.25
v = 45.8 m/s

Therefore the bullet must have hit the block of wood at a speed of 45.8 m/s
 
  • #3
1) CoolBlueR, do not post your question more than once. The appropriate place to post homework questions is here, in the homework help forum.

2) greybird, do not give away answers. This does not help the student. You should instead guide the student with thoughtful advice and hints about what to do next, filling in the steps for him/her only when he/she cannot do it independently.

- Warren
 

1. How do you calculate the initial speed of a 5.5g bullet impacting a wood block?

The initial speed can be calculated using the equation v = √(2gh), where v is the initial speed, g is the acceleration due to gravity (9.8 m/s²), and h is the height of the wood block.

2. What is the mass of the bullet used in this experiment?

The mass of the bullet is 5.5 grams, as stated in the title of the experiment.

3. How do you measure the impact of the bullet on the wood block?

The impact of the bullet on the wood block can be measured using a high-speed camera and analyzing the footage frame by frame to determine the distance the wood block moved upon impact.

4. What factors can affect the accuracy of the initial speed calculation?

The accuracy of the initial speed calculation can be affected by factors such as air resistance, imperfections in the wood block, and variations in the bullet's mass or shape.

5. Is there a difference in initial speed when using different types of bullets?

Yes, the initial speed may vary depending on the type of bullet used, as different bullets have different masses, shapes, and levels of aerodynamic efficiency.

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