Plank Equilibrium After Mass Movement · PhysicsBowl 2016 #20
Physics · mechanics
Problem
A uniform 10.0m long plank is pivoted about its center of gravity. A mass M1 then is placed at the left edge of the plank and a second mass M2 is placed 1.0m from the right end. This system is in static equilibrium (shown). If each mass now is moved 2.0m closer to the center of the plank, which one of the following choices best describes the subsequent motion of the plank?
(A) The plank remains in static equilibrium.
(B) The plank rotates at constant angular speed until the right side reaches the ground.
(C) The plank rotates at constant angular speed until the left side reaches the ground.
(D) The plank angularly accelerates until the right side reaches the ground.
(E) The plank angularly accelerates until the left side reaches the ground.
[Figure: Balanced plank with masses on pivot]