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9th Class Science Time and Motion Question Bank Motion

  • question_answer
    Displacement y (in m) of a body varies with time t (in sec.) as y = \[=\frac{-2}{3}{{t}^{2}}+16t+2\] How long does the body take to come to rest?

    A)  8 sec                                    

    B)  10 sec

    C)  12 sec                                    

    D)  16 sec

    Correct Answer: C

    Solution :

    Given,   \[y=\frac{-2}{3}{{t}^{2}}+16t+2\] Comparing it with\[y=\frac{1}{2}a{{t}^{2}}+ut\] we get   \[u=16\] and       \[\frac{1}{2}a=\frac{-2}{3}\],    \[\Rightarrow \]   \[a=\frac{-4}{3}\] Now      \[v=u+at\] \[\therefore \]      \[0=16-\frac{4}{3}t\] \[\Rightarrow \]   \[t=\mathbf{12}\,\,\mathbf{sec}\]


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