A stone is fastened to one end of a string and is whirled in a verticla circle of radius R. Find the minimum speed the stone can have at the highest point of the circle.

Explanation

To find the minimum speed of a stone at the highest point of a vertical circle, we can follow these steps:

### Step 1: Understand the Forces at the Highest Point
At the highest point of the vertical circle, two forces act on the stone: the gravitational force (mg) acting downward and the tension (T) in the string also acting downward. The net force towards the center of the circle is the sum of these two forces.

### Step 2: Apply Newton's Second Law
According to Newton's second law, the net centripetal force required to keep the stone moving in a circular path is given by:
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