KVPY Sample Paper KVPY Stream-SX Model Paper-27

  • question_answer
    A car accelerates from rest at a constant rate \[\alpha \] for some time, after which it decelerates at s constant rate \[\beta \] to come to rest. If total time a motion is t, then its displacement:

    A) \[\frac{\alpha +\beta {{t}^{2}}}{\left( \alpha +\beta  \right)}\]

    B) \[\frac{\alpha \beta {{t}^{2}}}{2\left( \alpha +\beta  \right)}\]

    C) \[\frac{{{\alpha }^{2}}t}{\left( \alpha +\beta  \right)}\]

    D) \[\frac{{{\beta }^{2}}{{t}^{2}}}{2\left( \alpha +\beta  \right)}\]

    Correct Answer: B

    Solution :

    If \[{{t}_{1}}\] is the time of acceleration, then
                \[\alpha {{t}_{1}}=\beta \left( t-{{t}_{1}} \right)\Rightarrow {{t}_{1}}=\frac{\beta t}{\alpha +\beta }\]
                \[\therefore \]\[{{v}_{\max }}=\alpha {{t}_{1}}=\frac{\alpha \beta t}{\alpha +\beta },\]
                \[s=\frac{1}{2}{{v}_{\max }}t.=\frac{\alpha \beta {{t}^{2}}}{2\left( \alpha +\beta  \right)}.\]


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