Consider the figure above consisting of three particles of mass m attached to a massless rod. Given an axis of rotation through point P, the rod rotates as shown in the figure. If the rod is released from rest in the horizontal position at t = 0. What is the angular acceleration of the system (rod and three particles) immediately after being released? Let d = 2.25 m.

Question

The distance between particles 1 and 2 is d. The distance between particles 2 and 3 is also d. Point p is between particles 2 and 3 and is a distance of (2d/3) from particle 3.

Thanks!

Answer 1

I total= I1+I2+I3 where Ii= 1/2 Mi distance^2, where distance is the distance from each Mi to P.

NetMoments=Itotal*angacceleration
now on writing Net moments, each of the three moments will be mass*g*distancefromP
the MUST here is to make clockwise moments+, ccw-.
solve for ang acceleration.

Answer 2

Why would clockwise moments be positive in this case?