9th Class Science Work and energy Question Bank Work Power and Energy IIT JEE Objective Problems

  • question_answer
    If the velocity of a car is trebled its K.E. is

    A)  doubled            

    B)  tripled

    C)  increase 9 times 

    D)  increase 15 times

    Correct Answer: C

    Solution :

      Given, \[{{v}_{1}}=v\,\,m/s\,\,\,{{v}_{2}}=3\,\,m/sK.E.=?\] We know, \[K.E.=\frac{1}{2}m{{V}^{2}}\] \[\Rightarrow K.E.\propto {{v}^{2}}\](\[\because \]The body is same therefore ?m? is constant) \[\therefore \,\,K.E{{.}_{1}}={{v}_{2}}\]                ???..(1) and \[K.E{{.}_{2}}={{(3v)}^{2}}=9{{v}^{2}}\]  ???..(2) Dividing equation (2) by (1) we get, \[\frac{K.{{E}_{2}}}{K.{{E}_{1}}}=\frac{9{{v}^{2}}}{{{v}^{2}}}=\frac{9}{1}\] \[\therefore \,\,K.{{E}_{2}}:\,K.{{E}_{1}}=9:1\] Therefore, K.E is increases 9 times.         


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