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
v=√2g=4.42

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
Mentor
45,379
1,758


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

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