question_answer

                Three identical metal balls each of radius r are placed touching each other on a horizontal surface such that an equilateral triangle is formed with centres of three balls joined. The centre of mass of the system is located at:

A)                                                                                                                                                                            horizontal surface                                                           

B)                 centre of one of the balls

C)                 line joining the centres of any two balls

D)                 point of intersection of the medians

Correct Answer: D

Solution :

                The whole mass of the ball will be concentrated at the centre of the ball. All the three balls are identical, i.e., the balls have same mass. On each vertex of equilateral triangle PQR, same mass is kept. Therefore, centre of mass of the triangle is the centre of mass of the system which is point of intersection of the medians of the triangle.