A stone of mass 0.4 kg is tied to a string and rotated in a vertical circle of radius 1.2 m . Calculate the speed of the stone for which the tension in the string is zero at the highest point of the circle . What is the tension at the lowest point in this case ?

Explanation

To solve the problem step by step, we need to calculate the speed of the stone when the tension in the string is zero at the highest point of the vertical circle and then determine the tension at the lowest point.

### Step 1: Understanding Forces at the Highest Point
At the highest point of the vertical circle, the only forces acting on the stone are its weight (mg) and the tension (T) in the string. For the tension to be zero, the centripetal force required to keep the stone moving in a circle must be provided entirely by the weight of the stone.

**Equation:**
\[ mg = \frac{mv^2}{r} \]

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