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

  • question_answer
    A stone dropped from a building of height h and it reaches after t seconds on earth. From the same building if two stones are thrown (one upwards and other downwards) with the same velocity u and they reach the earth surface after \[{{t}_{1}}\] and \[{{t}_{2}}\] seconds, respectively, then

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

    B) \[t=\frac{{{t}_{1}}+{{t}_{2}}}{2}\]

    C) \[t=\sqrt{{{t}_{1}}{{t}_{2}}}\]

    D) \[t_{1}^{2}=t_{2}^{2}\]

    Correct Answer: C

    Solution :

    [c] For first case of dropping \[h=\frac{1}{2}g{{t}^{2}}\]
    For second case of downward throwing,
    \[h=-u{{t}_{1}}+\frac{1}{2}gt_{1}^{2}=\frac{1}{2}g{{t}^{2}}\] \[\Rightarrow \]            \[-u{{t}_{1}}=\frac{1}{2}g({{t}^{2}}-t_{1}^{2})\]
    For third case of upward throwing,
    \[h=u{{t}_{2}}+\frac{1}{2}gt_{2}^{2}=\frac{1}{2}g{{t}^{2}}\]\[\Rightarrow \]          \[u{{t}_{2}}=\frac{1}{2}g({{t}^{2}}-t_{2}^{2})\]
    On solving these two equations: \[-\frac{{{t}_{1}}}{{{t}_{2}}}=\frac{{{t}^{2}}-t_{1}^{2}}{{{t}^{2}}-t_{2}^{2}}\]
    \[\Rightarrow \]            \[t=\sqrt{{{t}_{1}}{{t}_{2}}}\]


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