Three masses, each equal to M, are placed at the three corners of a square of side a. the force of attraction on unit mass at the fourth corner will be

Explanation

To find the force of attraction on a unit mass placed at the fourth corner of a square formed by three masses (each of mass M) at the other three corners, we can follow these steps:

### Step 1: Identify the positions of the masses
Let's denote the corners of the square as follows:
- Mass at corner A (0, 0): M
- Mass at corner B (a, 0): M
- Mass at corner C (0, a): M
- Unit mass at corner D (a, a): 1
...