A particle of mass 2 kg is moving such that at time t, its position, in meter, is given by r(t) = 5i - 2t²j. The angular momentum of the particle at t = 2s about the origin in kg m 2 s -1 is: (a) -80k (b) (10i - 16j) (c) -40k (d) 40k

Answer: (a). v=-4t j. At t=2: r=5 i-8 j, v=-8 j. L=m( r× v)=2[(5)(-8)-(-8)(0)] k L=-80 k So the answer is (a) -80 k.

A particle of mass 2 kg is moving such that at time t, its position… | JEE Main 2013 (23 Apr, Shift 1)

Q77JEE Main 2013 · 23 APR · SHIFT 1Medium

Angular Momentum & its Conservation

A particle of mass 2 kg is moving such that at time t, its position, in meter, is given by $\vec{r}(t) = 5\hat{i} - 2t^{2}\hat{j}$ . The angular momentum of the particle at $t = 2s$ about the origin in kg m $2$ s $-1$ is:

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Answer: (a)

$\vec v=-4t\hat j$ . At $t=2$ : $\vec r=5\hat i-8\hat j$ , $\vec v=-8\hat j$ .
$\vec L=m(\vec r\times\vec v)=2[(5)(-8)-(-8)(0)]\hat k$
$\vec L=-80\hat k$
So the answer is (a) $-80\hat k$ .

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Angular Momentum & its Conservation question from JEE Main 2013 (23 Apr, Shift 1)

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