JEE Main & Advanced Physics Two Dimensional Motion Question Bank Self Evaluation Test - Motion in a Plane

  • question_answer
    If \[|\vec{a}|\,=4,\,\,|\vec{b}|\,=2\] and the angle between \[\vec{a}\] and \[\vec{b}\] is \[\pi /6\] then \[{{(\overrightarrow{a}\times \overrightarrow{b})}^{2}}\] is equal to

    A) 48        

    B)        16   

    C) 4                     

    D)        2

    Correct Answer: B

    Solution :

    [b] We have, \[\text{\vec{a}}\,\text{.\vec{b}}=|\vec{a}||\vec{b}|cos\frac{\pi }{6}\]\[=4\times 2\times \frac{\sqrt{3}}{2}=4\sqrt{3}.\] \[\text{Now, }{{\left( \text{\vec{a}}\times \text{\vec{b}} \right)}^{2}}+{{\left( \text{\vec{a}}\,\text{.}\,\text{\vec{b}} \right)}^{2}}={{\text{a}}^{2}}{{\text{b}}^{2}};\]\[\Rightarrow {{\left( \text{\vec{a}}\times \text{\vec{b}} \right)}^{2}}+48=16\times 4\Rightarrow {{\left( \text{\vec{a}}\times \text{\vec{b}} \right)}^{2}}=16\]


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