## Question

A string can withstand a tension of 25 N. What is the greatest speed at which a body of mass 1 kg can be whirled in a horizontal circle using a 1 m length of a string?

### Solution

Since the stone is whirled in a horizontal circle, the gravity, acting vertically downwards, has no effect on the motion. If *v* is the greatest speed with which the body can be whirled, the maximum centripetal force (or tension) in the string is which must balance a force of 25 N. Thus

Which gives

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