9th Class Science Time and Motion Question Bank MCQs - Motion

  • question_answer
    A point object transverses half the distance with velocity \[{{v}_{0}}\]. The remaining part of the distance is covered with velocity \[{{v}_{1}}\] for the half of the time and with velocity \[{{v}_{2}}\] for the rest half. The average velocity of the object for the whole journey is

    A) \[2{{V}_{1}}\left( {{V}_{0}}+{{V}_{2}} \right)/\left( {{V}_{0}}+2{{V}_{1}}+2{{V}_{2}} \right)\]

    B) \[2{{V}_{0}}\left( {{V}_{0}}+{{V}_{1}} \right)/\left( {{V}_{0}}+{{V}_{1}}+{{V}_{2}} \right)\]

    C) \[2{{V}_{0}}\left( {{V}_{1}}+{{V}_{2}} \right)/\left( {{V}_{1}}+{{V}_{2}}+2{{V}_{0}} \right)\]

    D) \[2{{V}_{2}}\left( {{V}_{0}}+{{V}_{1}} \right)/\left( {{V}_{1}}+2{{V}_{2}}+{{V}_{0}} \right)\]

    Correct Answer: C

    Solution :

    [c] Let s be the total displacement, then
    \[=\frac{s}{2}={{v}_{0}}{{t}_{2}}+\operatorname{or}\ {{t}_{1}}=\frac{s}{2{{v}_{0}}}\]
              and \[=\frac{s}{2}={{v}_{1}}{{t}_{2}}+{{v}_{2}}\ {{t}_{3}}=({{v}_{1}}+{{v}_{2}}){{t}_{2}}\ \ \ \ \ \ \ (\because {{t}_{2}}={{t}_{3}})\]
    \[\therefore \operatorname{Average} velocity=\frac{Total displacement }{Total time}\]
    \[=\frac{s}{{{t}_{1}}+{{t}_{2}}+{{t}_{3}}}=\frac{s}{\frac{s}{2{{v}_{0}}}+\frac{s}{({{v}_{1}}+{{v}_{2}})}}\]
    \[=\frac{2{{v}_{0}}({{v}_{1}}+{{v}_{2}})}{{{v}_{1}}+{{v}_{2}}+2{{v}_{0}}}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner