question_answer

A particle of mass\[m=5\]units is moving with a uniform speed \[v=3\sqrt{2}\]m in the\[XOY\]plane along the line\[Y=X+4\]. The magnitude of the angular momentum about origin is:

A)  zero                     

B)         60 unit

C)  7.5 unit               

D)        \[40\sqrt{2}\]unit

E)  3.0 unit

Correct Answer: B

Solution :

Angular momentum about origin \[|\overrightarrow{L}|=|\overrightarrow{r}\times m\overrightarrow{v}|\]                 \[=(4\cos 45{}^\circ )\times (5)\times 3\sqrt{2}\]                 \[=\frac{4}{\sqrt{2}}\times 5\times 3\sqrt{2}\] \[|\overrightarrow{L}|=60\text{ }unit\]