Machine-translated by Google. Questions are authored in English.
Top

Discussion

Which of the following statements is correct ?

  • A.A system of \(n\) particles can have infinite degrees of freedom
  • B.A system of \(n\) particles with \(k\) holonomic constraints has \(3n - k\) degrees of freedom
  • C.A system of \(n\) particles with \(k\) constraints has \(n - k\) degrees of freedom
  • D.A system of \(n\) particles has 6 degrees of freedom

Answer: B

The correct statement is that \(n\) particles with \(k\) holonomic constraints have \(3n - k\) degrees of freedom.

Each free particle in space needs three coordinates, so \(n\) particles need \(3n\). A holonomic constraint is an equation \(f(\mathbf{r}_{1}, \ldots, \mathbf{r}_{n}, t) = 0\) among the coordinates, and each independent one lets us eliminate one coordinate. So \(3n - k\) independent generalised coordinates remain.

A finite system of particles cannot have infinitely many degrees of freedom (that needs a continuum). \(n - k\) forgets the three dimensions of space, and 6 is the number for a single rigid body, not for \(n\) particles in general.

No comment is present. Be the first to comment.
Loading…

Post your comment

Please log in or register to post a comment.