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Systems of Particles and Rotational Motion — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysicsSystems of Particles and Rotational Motion1 Mark
MCQ
A particle moves on a straight line with a uniform velocity. Its angular momentum:
  • A
    About any given point remains constant.
  • B
    Is zero about a point on the straight line.
  • C
    Is not zero about a point away from the straight line.
  • ✓
    All of the above.
✓

Answer

Correct option: D.
All of the above.
Angular momentum $=\text{m}\Big(\overrightarrow{\text{r}}\times\overrightarrow{\text{v}}\Big)$
If the point is on the straight line, $\overrightarrow{\text{r}}$ and $\overrightarrow{\text{v}}$ will have the same direction and their cross product will be zero. Hence, angular momentum is zero.
If the point is not on the straight line, $\overrightarrow{\text{r}}$ and $\overrightarrow{\text{v}}$ will not have the same direction and their cross product will not be zero. Hence, angular momentum is non$-$zero.
No external torque is applied on the body; therefore, its angular momentum about any given point remains constant.

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