NEET Sample Paper NEET Sample Test Paper-83

  • question_answer
    A particle is moving in X-Y plane, when position vectors are given as a function of time  \[x= 2.0\,m\,-\,\left( 0.25 m/{{s}^{2}} \right){{t}^{2}}\] and \[\operatorname{y}= \left( 1.0 m/s \right)t\,+\,\,(0.025m/{{s}^{2}}){{t}^{2}}\] Find the unit vector along particle velocity at\[\operatorname{t}= 2s\].

    A)  \[\frac{\hat{i}-2.2\,\hat{j}}{2.42}\]                    

    B)  \[\frac{-\,\hat{i}+1.3\,\hat{j}}{1.64}\]

    C)  \[\frac{\hat{j}+\,\hat{k}}{\sqrt{2}}\]                 

    D)  None of these

    Correct Answer: B

    Solution :

    \[x=2-0.25\,{{t}^{2}}\] \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,\,{{v}_{x}}=\frac{dx}{dt}=\,\,-\,0.5\,t\] and     \[\operatorname{y} =\,\,t+\,\,0.025 {{t}^{2}}\] \[{{v}_{\operatorname{y}}} =\,\,\frac{dy}{dt}=1+\,\,0.075 {{t}^{2}}\] \[{{\operatorname{v}}_{x/t=2}}=\,\,-1\,m\,/s,\,{{v}_{y/t\,=\,2}}\,\,=\,\,1.3\,\,m/s\] \[\therefore ~~v=\,\,v\times \hat{i}\,\,+\,\,{{v}_{y}}\,\hat{j}\,\,=\,\,-\,\hat{i}\,\,+\,\,1.3 \hat{j}\] \[\hat{v}=\frac{v}{\left| v \right|}=\frac{(-\hat{i}+1.3\hat{j})}{1.64}\]


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