Bullet in Block- 2D Projectiles w/ Motion

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Homework Help Overview

The problem involves a bullet colliding with a block on a frictionless table, leading to a discussion on the conservation of momentum and projectile motion. The bullet's mass and the block's mass are provided, along with the height of the table and the distance the block lands from the table's edge.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants discuss separating the problem into horizontal and vertical components, using kinematic equations to find time and initial velocities. Questions arise regarding the correct form of the collision equation and the definitions of variables involved.

Discussion Status

Some participants have provided guidance on the correct collision equation to use, while others are clarifying the definitions of variables related to the collision. There is an ongoing exploration of how to set up the equations properly without reaching a consensus yet.

Contextual Notes

There is a mention of confusion regarding the collision equation used by the original poster, indicating a potential misunderstanding of the conservation of momentum principles. The problem setup involves assumptions about the initial conditions of the block and bullet.

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Homework Statement



A(n) 9 g bullet is fired into a 396 g block
that is initially at rest at the edge of a frictionless table of height 0.9 m. The bullet remains
in the block, and after impact the block lands
2.3 m from the bottom of the table.
The acceleration of gravity is 9.8 m/s.

Homework Equations



ΔX = Vi(t) + (1/2)(a)(t^2)

m(Vf-Vi) = -m(Vf-Vi)

The Attempt at a Solution


I separated the equation into vertical and horizontal parts.

Horizontal: ΔX=2.3, a = 0 m/s/s
Vertical: ΔY= .9, a= -9.8 m/s/s, Vi = 0 m/s (because it is launched horizontally).

Using the kinematic equation ΔX = Vi(t) + (1/2)(a)(t^2) to solve for the vertical time:
t = 0.4285714286 seconds

Since the vertical time is equal to the horizontal time, I plugged this time into the same kinematic equation to solve for the horizontal Vi:
Vi = 5.366666667 m/s

Now, I know you need to use the collision equation to solve for the initial velocity in the bullet, but I do not know how to set it up...
I have this so far

9(5.366666667-vi)=-____?_____

Thank you for the help :)
 
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m(Vf-Vi) = -m(Vf-Vi) That is not the collision equation I am familiar with. With just a single m, it suggests a collision involving a single object, an oxymoron if I've ever heard one. Try m1v1i+m2v2i=m1v1f+m2v2f
You should then be able to quickly simplify one side by equating one velocity with another, and it will all fall out from there.
 
Barakn said:
m(Vf-Vi) = -m(Vf-Vi) That is not the collision equation I am familiar with. With just a single m, it suggests a collision involving a single object, an oxymoron if I've ever heard one. Try m1v1i+m2v2i=m1v1f+m2v2f
You should then be able to quickly simplify one side by equating one velocity with another, and it will all fall out from there.
What would m2, v2i, and v2f be?
 
m2 would be mass of the block, v2i is the initial velocity of the block, and v2f is the final velocity of the block
 
I got it, thanks!
 

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