KVPY Sample Paper KVPY Stream-SX Model Paper-22

  • question_answer
    A strip of wood of length l is placed on a smooth horizontal surface. An insect starts from one end of the strip, walks with constant velocity and reaches the other end in time \[{{t}_{1}}\]. It then flies off vertically. The strip moves a further distance l in time \[{{t}_{2}}.\]

    A) \[{{t}_{1}}={{t}_{2}}\]

    B) \[{{t}_{1}}>{{t}_{2}}\]

    C) \[{{t}_{1}}<{{t}_{2}}\]

    D) none

    Correct Answer: C

    Solution :

    If \[v\] is the velocity of insect and \[v\] is the velocity of strip (opposite direction), then \[l=\left( v+u \right){{t}_{1\,}}\]
    \[\therefore {{t}_{1}}=\frac{\ell }{\left( v+u \right)}\]
    When insect fly off, \[{{t}_{2}}=\frac{\ell }{u}\]
    Clearly, \[{{t}_{2}}>{{t}_{1}}\]

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