- #1

- 4

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## Homework Statement

A rod of length D sits at rest on a friction less table. A ball of mass M strikes the end of the rod with a speed V and rebounds with a speed 3v/4 causing the rod to rotate counterclockwise around a fixed axis at one end. The rotational inertia of the rod is I

## Homework Equations

Li = Lf

## The Attempt at a Solution

the question is :

**What is the angular velocity ω of the rod after the collision?**We know that the initial angular momentum is equal to the final angular momentum so i started with the ball because it's the only object in our system that has initial angular momentum:

MvD = -3MvD/4 + IW

doing some algebra:

MvD * 4 = -3MvD + IW

4MvD + 3MvD = IW

7MvD = IW

W = 7MvD/I

But the correct answer is :

7MvD/4I

my question where did the 4 come from ?

is my math Wrong ?