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CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2008

  • question_answer
    A stone is thrown vertically upwards and the height x ft reached by the stone in t seconds is given by\[x=80t-16{{t}^{2}}\]. The stone reaches the maximum height in

    A)  \[2s\]                                  

    B)  \[2.5s\]

    C)  \[3s\]                                  

    D)  \[1.5s\]

    Correct Answer: B

    Solution :

    Given,  \[x=80\,t-16{{t}^{2}}\] On differentiating w.r.t. t, we get \[\frac{dx}{dt}=80-32t\] Since, the stone reaches the maximum height, then velocity will be zero \[\left( ie,\,\,\frac{dx}{dt}=0 \right)\] \[\therefore \]  \[80-32t=0\] \[\Rightarrow \]               \[t=2.5s\]


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