- #1

jisbon

- 476

- 30

- Homework Statement
- Thin rod of mass 5kg and length 2m rotates with an angular velocity of 1.5rad/s and translates with 2m/s towards another uniform rod with mass 20kg and length 5m. They collide and stick together such that the centres and axes align. Find angular velocity after collision.

- Relevant Equations
- NIL

Hi,

Since this is a question about COAM (Conservation of Angular Momentum), I will assume I can leave out the part on translation and just use the formula below:

##Initial Angular Momentum= Final Angular Momentum##

whereby ##I = \frac {1}{12}ML^2## (of rod)

So,

##\frac {1}{12}ML^2(1.5)=\frac {1}{12}(m+M)L^2(x)##

##\frac {1}{12}(5)2^2(1.5)=\frac {1}{12}(25)5^2(x)##

I find x to be 0.048rad/s, which appears to be wrong. Correct is 0.0577rad/s

Any ideas on this?

Since this is a question about COAM (Conservation of Angular Momentum), I will assume I can leave out the part on translation and just use the formula below:

##Initial Angular Momentum= Final Angular Momentum##

whereby ##I = \frac {1}{12}ML^2## (of rod)

So,

##\frac {1}{12}ML^2(1.5)=\frac {1}{12}(m+M)L^2(x)##

##\frac {1}{12}(5)2^2(1.5)=\frac {1}{12}(25)5^2(x)##

I find x to be 0.048rad/s, which appears to be wrong. Correct is 0.0577rad/s

Any ideas on this?