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

  • question_answer
    A ball is released from the top of a tower of height h metre. It takes T sec to reach the ground. What is the position of the ball in \[\frac{T}{3}\] sec?

    A) \[\frac{h}{9}\] m from the ground

    B) \[\frac{7h}{9}\] m from the ground

    C) \[\frac{8h}{9}\]m from the ground

    D) \[\frac{17h}{18}\] m from the ground

    Correct Answer: C

    Solution :

    [c] As, initial velocity of ball is zero.
    \[\because \ \ \ \ \ \ \ \ \ \ \ \ \ s=ut+\frac{1}{2}g{{t}^{2}}\]
    \[\Rightarrow \ \ \ \ \ \ \ \ \ \ \ \ \ h=\frac{1}{2}g{{T}^{2}}\]
    \[\operatorname{In}=\frac{T}{3}\sec ,\]
    \[{{h}_{1}}=\frac{1}{2}g{{\left( \frac{T}{3} \right)}^{2}}=\frac{1}{2}g\left( \frac{{{T}^{2}}}{9} \right)\]
    From Eqs. (i) and (ii), we get
    \[{{h}_{1}}=\frac{h}{9}\]
    Distance of ball from ground =\[h=\frac{h}{9}=\frac{8h}{9}\operatorname{m}\]


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