JEE Main & Advanced Physics Motion in a Straight Line / सरल रेखा में गति Sample Paper Topic Test - One Dimensional Motion

  • question_answer
    A point moves with uniform acceleration and \[{{v}_{1}},\text{ }{{v}_{2}},\text{ }{{v}_{3}}\] denote the average velocities in three successive intervals of time \[{{t}_{1}},\text{ }{{t}_{2}},\text{ }{{t}_{3}}\]. Which of the following relations is correct?

    A) \[({{v}_{1}}{{v}_{2}}):({{v}_{2}}{{v}_{3}})=({{t}_{1}}{{t}_{2}}):\text{(}{{t}_{2}}+{{t}_{3}})\]

    B) \[({{v}_{1}}{{v}_{2}}):({{v}_{2}}{{v}_{3}})=({{t}_{1}}+{{t}_{2}}):\text{(}{{t}_{2}}+{{t}_{3}})\]

    C) \[({{v}_{1}}{{v}_{2}}):({{v}_{2}}{{v}_{2}})=({{t}_{1}}-{{t}_{2}}):\text{(}{{t}_{2}}-{{t}_{3}})\]

    D) \[({{v}_{1}}{{v}_{2}}):({{v}_{2}}+{{v}_{3}})=({{t}_{1}}-{{t}_{2}}):\text{(}{{t}_{2}}+{{t}_{3}})\]

    Correct Answer: B

    Solution :

    [b] Suppose velocity at O = zero
    As average velocity in interval \[{{t}_{1}}\] is \[{{v}_{1}}\].
           velocity at \[A={{v}_{1}}\]
    As average velocity in interval \[{{t}_{2}}\] is \[{{v}_{2}},\]
          velocity at \[B=({{v}_{2}}{{v}_{1}})\]
    As average velocity in interval \[{{t}_{3}}\] is \[{{v}_{3}},\] velocity at \[C\text{ }({{v}_{3}}{{v}_{2}}+\text{ }{{v}_{1}})\]
    Using   \[v=u+at\]
    \[{{v}_{1}}=0+a{{t}_{1}}\] ....(i)
    \[({{v}_{2}}{{v}_{1}})=0+a({{t}_{1}}+\text{ }{{t}_{2}})\] ....(ii)
    \[({{v}_{3}}{{v}_{2}}+{{v}_{1}})=0+a({{t}_{1}}+{{t}_{2}}+{{t}_{3}})\] ....(iii)
    Subtract Eq. (i) from Eq. (iii)  
    \[({{v}_{3}}{{v}_{2}})=a({{t}_{2}}+{{t}_{3}})\] ....(iv)
    Divided Eq. (ii) by Eq. (iv)
    \[\frac{({{v}_{2}}-\,{{v}_{1}})}{({{v}_{3}}-{{v}_{2}})}\,=\,\frac{a({{t}_{1}}+{{t}_{2}})}{a({{t}_{2}}+{{t}_{3}})}\]
    \[\frac{({{v}_{1}}-\,{{v}_{2}})}{({{v}_{2}}-{{v}_{3}})}\,=\,\frac{{{t}_{1}}+{{t}_{2}}}{{{t}_{2}}+{{t}_{3}}}\]


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