NEET Sample Paper NEET Sample Test Paper-39

  • question_answer A force \[\vec{F}=\alpha \hat{i}+3\hat{j}+6\hat{k}\]is acting at a point\[\vec{r}=2\hat{i}-6\hat{j}-12\hat{k}.\] The value of a for which angular momentum about origin is conserved is

    A)  1             

    B)  -1

    C)  2             

    D)  zero            

    Correct Answer: B

    Solution :

    Angular momentum will be conserved if net torque acting on the system becomes zero. Given force acting \[\vec{F}=\alpha \hat{i}+3\hat{j}+6\hat{k}\]       (i) and \[\vec{r}=2\hat{i}-6\hat{j}-12\hat{k}=-2(-\hat{i}+3\hat{j}+6\hat{k})\]      (ii) If torque becomes zero then \[\vec{r}\times \vec{F}=0\] If \[\alpha =-1\]then, \[\vec{r}\times \vec{F}=0\]

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