Manipal Engineering Manipal Engineering Solved Paper-2009

  • question_answer
    A body of mass m moving along a straight line covers half the distance with a speed of\[2m{{s}^{-1}}\]. The remaining half of the distance is covered in two equal time intervals with a speed of \[3m{{s}^{-1}}\] and \[5m{{s}^{-1}}\] respectively. The average speed of the particle for the entire journey is

    A)  \[\frac{3}{8}m{{s}^{-1}}\]                           

    B) \[\frac{8}{3}m{{s}^{-1}}\]

    C)  \[\frac{4}{3}m{{s}^{-1}}\]          

    D)         \[\frac{16}{3}m{{s}^{-1}}\]

    Correct Answer: B

    Solution :

                    Let the total distance travelled by the body is 25. If\[{{t}_{1}}\]is the time taken by the body to travel first half of the distance, then                 \[{{t}_{1}}=\frac{S}{2}\] Let\[{{t}_{2}}\]be the time taken by the body for each time interval for the remaining half journey. \[\therefore \]  \[S=3{{t}_{2}}+5{{t}_{2}}=8{{t}_{2}}\] So, average speed\[\text{=}\frac{\text{Total}\,\,\text{distance}\,\,\text{travelled}}{\text{Total}\,\,\text{timetaken}}\]                 \[=\frac{2S}{{{t}_{1}}+2{{t}_{2}}}\]                 \[=\frac{2S}{\frac{S}{2}+\frac{S}{4}}\]                 \[=\frac{8}{3}m{{s}^{-1}}\]


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