The locus of a point on a string unwound from a circular disc is

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ISRO VSSC Technical Assistant Mechanical 9 June 2019 Official Paper
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  1. A circle
  2. An involute
  3. A cycloid
  4. A parabola

Answer (Detailed Solution Below)

Option 2 : An involute
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Detailed Solution

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Explanation:

By definition we have the profile created by a fixed point on the string while it unwraps from a disk is Involute.

  • In the gear profile, this involute profile starts from the base circle.

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Important points about the Involute created by disk and string.

  • Not only the endpoint of string but all the intermediate point after unwrapping from the disk follows involute profile.
  • The string needs to be in tight position throughout the unwrapping.

Additional Information

Cycloid

A cycloid is a curve traced by a point on the circumference of a circle which rolls without slipping on a fixed straight line.

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