Tilting

If a rod is supported at two points A and B then when the rod is about to tilt about B the normal

reaction at A will be 0.

Example: A uniform plank PQ of mass 8 kg rests on two supports at A and B.

PQ = 2 m, PA = 0.6 m and AB =0.7 m. A mass M kg is placed at X on the rod between B

and Q at a distance of 0.5 m from B.

The rod is on the point of tilting about B: find the value of M.

Solution:

DRAW A DIAGRAM SHOWING ALL FORCES

The centre of mass, G, will be at mid point, ⇒ PG = 1 m.