Question

Four bodies of equal mass start moving with same speed as shown in the figure. In which of the following combination the centre of mass will remain at origin:

• A. c and d
• B. a and b
• C. a and d
• D. b and d

Answer 1

Answer: (C)

a and d

Answer 2

Centre of mass lies always on the line that joins the two particles. For the combination cd and ab this line does not pass through the origin. For combination bd, and ab this line does not pass through the origin. For combination bd, initially it pass through the origin but later on it moves toward negative x-axis. But for combination ac it will always pass through origin. So we can say that centre of mass of this combination will remain at origin.