JEE Main & Advanced Physics Work, Energy, Power & Collision / कार्य, ऊर्जा और शक्ति Question Bank Self Evaluation Test - Work, Energy and Power

  • question_answer
    A body of mass 1 kg begins to move under the action of a time dependent force\[\vec{F}=\left( 2t\hat{i}+3{{t}^{2}}\hat{j} \right]) N,\], where \[\hat{i} and \hat{j}\]are unit vectors alogn x and y axis. What power will be developed by the force at the time t?

    A) \[\left( 2{{t}^{2}}+3{{t}^{3}} \right)W\]

    B) \[\left( 2{{t}^{2}}+4{{t}^{4}} \right)W\]

    C) \[\left( 2{{t}^{3}}+3{{t}^{4}} \right)W\]

    D) \[\left( 2{{t}^{3}}+3{{t}^{5}} \right)W\]

    Correct Answer: D

    Solution :

    [d] Given force \[\vec{F}=2t\hat{i}+3{{t}^{2}}\hat{j}\] According to Newton's second law of motion, \[m\frac{d\vec{v}}{dt}=2t\hat{i}+3{{t}^{2}}\hat{j}\]               \[(m=1kg)\] \[\Rightarrow  \int\limits_{0}^{{\vec{v}}}{d\vec{v}} = \int\limits_{0}^{t}{\left( 2t\hat{i} + 3{{t}^{2}}\hat{j} \right)dt\Rightarrow  \vec{v} = {{t}^{2}}\hat{i} +{{t}^{3}}\hat{j}}\] Power \[\operatorname{P} = \vec{F}-\vec{v} \left( 2t\hat{i}+ 3{{t}^{2}}\hat{j} \right). \left( {{t}^{2}}\hat{i} +{{t}^{3}}\hat{j} \right)\] \[=\left( 2{{t}^{3}}+3{{t}^{5}} \right)W\]


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