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Why does a centripetal force change a body's direction but never its speed?
ABecause it acts along the motion
BBecause it is perpendicular to the motion
CBecause it is far too weak to matter
DBecause it acts for a very short time
Answer & Solution
Correct answer: B. Because it is perpendicular to the motion
1. The velocity of a body on a circle lies along the tangent to the path.
2. The centripetal force is always perpendicular to that path, pointing at the centre.
3. A force at right angles to the motion has no component along the direction of travel.
4. With nothing to speed the body up or slow it down, only the direction can change.
_Source: OpenStax College Physics (CC BY 4.0), Ch 6 "Uniform Circular Motion and Gravitation", section 6.3 Centripetal Force_
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