| Problem statement Solution video |
DISCUSSION THREAD
Ask and answer questions here. You learn both ways.
DISCUSSION and HINTS
Recall the definition of angular momentum of a particle P (of mass m) about a fixed point O: HO = m rP/O x vP.
For this problem, use this equation to find the angular momentum of the particle about the three fixed points A, B and C. Are any of these three values zero? If so, why does it equal zero?
Do we need to draw an FBD for this problem?
No. There are no forces involved here, just kinematics.
At point C, the radius and velocity are parallel, therefore the cross product is zero. What does that mean for point C?
If the position vector and velocity of P about C are parallel with each other this means the the velocity move along the position line. Which then means that the angle that the position vector make with an right angled axis never changes and therefore therefor the angular velocity about point C is zero.
If what you say is true, then r_P/C x v_P = 0, as you say. Therefore, the angular momentum would be zero, although neither r_P/C nor v_P are zero.