# Ballistic pendulum change in kinetic energy problem

• victoriafello
In summary, a bullet of mass M is fired into a block of wood of mass m, causing the wood to swing upwards by a height h. The change in kinetic energy from the bullet to the bullet+wood can be calculated using the equations for kinetic energy and initial velocity. However, there seems to be confusion about the correct formula for initial velocity, as it should be (m+M)/M*sqrt(2gh) instead of M*sqrt(2gh). This needs to be resolved quickly as the assignment is due tomorrow.
victoriafello

## Homework Statement

a bullet of mass M is fired into a block of wood of mass m, the bullet sticks in the wood and causes it to swing upwards by height h

calculate the change in kinetic energy from the bullet to the bullet+wood

## Homework Equations

kinetic energy = 1/2MV^2
V = SQRT (2gh)
Inital speed = m+M / m Sqrt(2gh)

so initial kinetic energy is 1/2 M m+M / m Sqrt(2gh)
final kinetic energy is 1/2 M + m SQRT (2GH)

## The Attempt at a Solution

i know i need to divide final EK by initial EK but i am not sure if i have all the equations correct as when i try and do this i can't get to an answer

can anyone help>

Since mass of the bullet is M, your expression for initial velocity is wrong. Check it.
They expect to find (initial KE - final KE)

rl.bhat said:
Since mass of the bullet is M, your expression for initial velocity is wrong. Check it.
They expect to find (initial KE - final KE)

i have had another look and I am not sure if i should cancel the m's as they don't apply yet this would give me

Ini Vel = M SQRT(2gh)

is this better ?

No.
Vi = (m+M)/M*sqrt(2gh)

ok then so where am i going wrong ? i have been thru my textbook and asked my teacher but i just can't get it right, i think the problem is with the formula for inital KE but however i go thru it i get the same result,

this needs to be in tomorrow so i am having a panic now

thanks

## What is a ballistic pendulum change in kinetic energy problem?

A ballistic pendulum change in kinetic energy problem is a physics problem that involves calculating the change in kinetic energy of a pendulum after it has been struck by a projectile. The projectile's initial velocity and mass are known, and the final height and angle of the pendulum are measured. This problem is commonly used to demonstrate the principles of conservation of energy and momentum.

## How do you calculate the change in kinetic energy in a ballistic pendulum problem?

The change in kinetic energy (ΔKE) can be calculated by subtracting the final kinetic energy from the initial kinetic energy. The initial kinetic energy is equal to 1/2 times the mass of the projectile times its initial velocity squared. The final kinetic energy is equal to 1/2 times the combined mass of the pendulum and projectile times the final velocity of the pendulum squared.

## What is the formula for calculating the final velocity of the pendulum in a ballistic pendulum problem?

The final velocity of the pendulum (vf) can be calculated using the principle of conservation of momentum. The formula is: vf = (m1v1 + m2v2) / (m1 + m2), where m1 is the mass of the projectile, v1 is its initial velocity, m2 is the mass of the pendulum, and v2 is the final velocity of the pendulum. This formula assumes that the projectile sticks to the pendulum after impact.

## What are the key assumptions in a ballistic pendulum change in kinetic energy problem?

There are several key assumptions in a ballistic pendulum problem. First, it is assumed that there is no energy lost due to friction or air resistance during the collision. Second, it is assumed that the projectile sticks to the pendulum after impact. Third, it is assumed that the pendulum is initially at rest and swings to a maximum height after impact.

## What is the real-world application of ballistic pendulum problems?

Ballistic pendulum problems have real-world applications in fields such as ballistics, forensics, and engineering. In ballistics, they can be used to study the effects of different types of ammunition on targets. In forensics, they can be used to determine the speed and angle of a bullet based on the trajectory of a pendulum. In engineering, they can be used to test the strength and impact resistance of materials.

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