A CRATE OF MESS 50KG IS LYING ON A 30DEGREE INCLINE, A STEEL BALL OF MASS 20KG IS ATTACHED TO THE CRATE WITH A ROPE.THE ROPE IS GOING OVER A FRICTIONLESS PULLEY.CALCULATE THE FRICTION COEFICIENT NEEDED SO THAT THE 50KG BLOCK STAYS AT REST.

Answer 1

Please remove your caps lock in future.

Perform a force balance. Let Us be the reuired static friction coefficient.

(static) friction force = steel ball weight

50 kg * g *cos30 * Us = 20 kg * g

Cancel out g; solve for Us.
It will be a lower limit