Rotational motion, energy conservation problem please help

  • #1
rotational motion, energy conservation problem URGENT please help

Homework Statement

A uniform rod of mass M=2 kg and length L = 2m is pivoted from its end. It has a point mass m=1 kg on its tip. It stars from rest at an angle of 30 degrees above horizontal. It falls under the influence of gravity. How fast is the tip m moving when the rod is horizontal at θ
= 0

Homework Equations

mgh = 1/2mv^2

The Attempt at a Solution

h= Lsinθ = 1
m cancels from both sides
so you're left with

BUT, the actual answer given is 4.8

Help please! I have a test in just a few hours and have been trying to figure this problem out for awhile! Thanks

Answers and Replies

  • #2
Doc Al

How would you write the rotational KE of the system? Also, what's the total change in gravitational PE as it falls?