# Perfectly inelastic collision problem, need some help

In summary, after the bullet impacts the block, the block is knocked off a 1m tall table and lands 2m away from where it started. The initial speed of the bullet is determined to be 143m/s.

## Homework Statement

An 8g bullet is fired into a 250g block that is initially at rest at the edge of a table of height 1m. The bullet remains in the block, and after the impact the block lands 2m from the bottom of the table. Determine the initial speed of the bullet. [To clarify, the block, after getting hit by the bullet, gets knocked off a 1m tall table and lands 2m away from where it started. no friction either.]

## Homework Equations

m1v1i + m2v2i = m1v1f + m2v2f
p=mv

## The Attempt at a Solution

before the collision, i have...

m1v1i + m2v2i = (m1+m2)vf

plug in the data...

(0.008)vi + 0 = (0.258)vf

and that's where I'm stumped. I tried using delta-y=v0*t + 1/2at^2 to solve for t and then plug into solve for the velocity in the x direction... (v=d/t)... and then using that as my vf to solve for my vi... and even though the answer LOOKED right (143 m/s) i got the strange feeling it was wrong. any suggestions or leads guys?

I tried using delta-y=v0*t + 1/2at^2 to solve for t and then plug into solve for the velocity in the x direction... (v=d/t)... and then using that as my vf to solve for my vi... and even though the answer LOOKED right (143 m/s) i got the strange feeling it was wrong. any suggestions or leads guys?
No suggestions or leads are required, your method and solution are perfect!

PhanthomJay said:

thank you!

and i can't believe i was right lol, i even went as far as erasing everything :'(

oh well, thanks a lot for the verifcation!

## What is a perfectly inelastic collision?

A perfectly inelastic collision is a type of collision where two objects stick together after impact and move as one object. In this type of collision, kinetic energy is not conserved and some energy is lost due to deformation or other factors.

## How is momentum conserved in a perfectly inelastic collision?

In a perfectly inelastic collision, momentum is conserved because the total momentum of the system before and after the collision remains the same. The objects may stick together and move with the same velocity, but the total momentum remains constant.

## What is the equation for calculating the final velocity in a perfectly inelastic collision?

The equation for calculating the final velocity in a perfectly inelastic collision is v = (m1v1 + m2v2) / (m1 + m2), where m1 and m2 are the masses of the objects and v1 and v2 are their initial velocities.

## Can a perfectly inelastic collision result in a decrease in kinetic energy?

Yes, a perfectly inelastic collision can result in a decrease in kinetic energy. This is because some of the initial kinetic energy is converted into other forms of energy, such as heat or sound, due to the deformation of the objects.

## What are some real-life examples of perfectly inelastic collisions?

Some real-life examples of perfectly inelastic collisions include a car crashing into a wall and sticking to it, a person catching a ball and holding onto it, and a bullet hitting a target and becoming embedded in it.

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