Problem statementSolution video |

**DISCUSSION THREAD**

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**DISCUSSION**

**Four-step plan**

**Step 1: FBD**

Draw a free-body diagram particles A and B, along with the bar, altogether. Is angular momentum for this system conserved? Why, or why not?

**Step 2: Kinetics - Angular impulse/momentum**

Write down the angular momentum for A, B and the bar individually, and then add together. For a particle A, for example, recall that angular momentum is given by * H_{O} = m r_{A/O} x v_{A}*. For a rigid body,

**H**_{O}= I_{O}**ω**. You will also need the coefficient of restitution equation relating the

*radial*(normal components here) components of velocity of A and B during impact.

* Step 3: Kinematics*For writing down the velocity of points A and B, a polar description is recommended. For example,

**v**_{A}= R_dot**e**_{R}+ Rω**e**_{θ}.**Step 4: Solve**

Solve your equations from Steps 2 and 3 for the velocity of P. Do not forget that A will have *both* radial and transverse components of velocity.

Sometimes I get confused when working with polar coordinates. Does A have velocity in both the e_phi and the e_R directions? And does B only have velocity in the e_phi direction?

B is "rigidly attached" to the end of the bar so it only has velocity in the e_phi direction. Since A can slide on the bar it has velocity in both directions.

Since Omega 1 isn't given a numerical value, should we leave it as a variable in our final answer?

Yeah, I think the only thing we can do is leave omega_1 as it is in our final answer.

Are we meant to use the kinematics equations to find the angular velocity or is there another way or working that out?