Particles of masses , and are placed on a line at , and . Find the -coordinate of their centre of mass.

Answer and explanation

Correct answer: D.

  1. Step 1: .
  2. Step 2: and , so m.
Answer
.
Why not the others: is what you get if you take a simple average of the positions. is what you get if you forget to divide by the total mass. is what you get if you divide by the sum of the positions.

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