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9th Class Science Gravitation and Floatation Question Bank Gravitation Summative Objective Problems

  • question_answer
    If the distance between the earth and the sun were half its present value, the number of days in a year would have been

    A)  64.5                      

    B)  129  

    C)              182.5                   

    D)  730

    Correct Answer: B

    Solution :

      According to Kepler?s law \[\frac{T_{1}^{2}}{T_{2}^{2}}=\frac{R_{1}^{3}}{R_{2}^{3}}{{T}_{1}}=365\,\,day{{T}_{2}}=?\] \[{{R}_{1}}=R{{R}_{2}}=\frac{R}{2}\] \[\Rightarrow {{T}_{2}}={{T}_{1}}{{\left( \frac{{{R}_{2}}}{{{R}_{1}}} \right)}^{3/2}}=365{{\left[ \frac{R/2}{R} \right]}^{3/2}}=129\,\,days\]


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