JEE Main & Advanced JEE Main Paper (Held On 15 April 2018) Slot-I

  • question_answer
    Take the mean distance of the moon and the sun from the earth to be \[0.4\times {{10}^{6}}km\]and \[150\times {{10}^{6}}km\] respectively. Their masses are \[8\times {{10}^{22}}kg\]and \[2\times {{10}^{30}}kg\] respectively. The radius of the earth is\[6400km\]. Let \[\Delta {{F}_{1}}\] be the difference in the forces exerted by the moon at the nearest and farthest points on the earth and \[\Delta {{F}_{2}}\] be the difference in the force exerted by the sun at the nearest and farthest points on the earth. Then, the number closest to \[\frac{\Delta {{F}_{1}}}{\Delta {{F}_{2}}}\] is:                         [JEE Online 15-04-2018]

    A) 2                                 

    B) 6         

    C) \[{{10}^{-2}}\]                    

    D) 0.6      

    Correct Answer: C

    Solution :

    \[\Delta {{F}_{1}}={{F}_{1}}-{{F}_{2}}\] \[\Delta {{F}_{2}}={{F}_{1}}^{'}-{{F}_{2}}^{'}\] \[\Delta {{F}_{1}}=\frac{G{{m}_{m}}{{m}_{e}}}{(0.4\times {{10}^{6}}-\operatorname{Re})}-\frac{G{{m}_{m}}{{m}_{e}}}{(0.4\times {{10}^{6}}+\operatorname{Re})}\] \[\Delta {{F}_{2}}=\frac{G{{m}_{m}}{{m}_{s}}}{(150\times {{10}^{6}}-\operatorname{Re})}-\frac{Gm{{e}_{m}}{{m}_{e}}}{(150\times {{10}^{6}}+\operatorname{Re})}\] \[\frac{\Delta {{F}_{1}}}{{{F}_{2}}}=\frac{G{{M}_{m}}Me\left\{ \frac{1}{0.4\times {{10}^{6}}-\operatorname{Re}}-\frac{1}{0.4\times {{10}^{6}}+\operatorname{Re}} \right\}}{G{{M}_{e}}Ms\left\{ \frac{1}{150\times {{10}^{6}}-\operatorname{Re}}-\frac{1}{150\times {{10}^{6}}+\operatorname{Re}} \right\}}\]          \[=\frac{\frac{Mm}{Ms}\left\{ \frac{0.4\times {{10}^{6}}+\operatorname{Re}-0.4\times {{10}^{6}}+\operatorname{Re}}{(0.4\times {{10}^{6}}-\operatorname{Re})(0.4\times {{10}^{6}}+\operatorname{Re})} \right\}}{\left\{ \frac{150\times {{10}^{6}}+\operatorname{Re}-150\times {{10}^{6}}+\operatorname{Re}}{(150\times {{10}^{6}}-\operatorname{Re})(150\times {{10}^{6}}+\operatorname{Re}} \right\}}\] \[\frac{Mm}{Ms}\times \frac{(150\times {{10}^{6}}-\operatorname{Re})(150\times {{10}^{6}}+\operatorname{Re})}{(0.4\times {{10}^{6}}-\operatorname{Re})(0.4\times {{10}^{6}}+\operatorname{Re}}=\frac{(150-.0064)(150+.0064)}{(0.4-.0064)(0.4+.0064)}\] \[=\frac{Mm}{Ms}\frac{149.99\times 150.0064}{0.3936\times .4064}\] \[=140657.633\times \frac{8\times {{10}^{22}}}{2\times {{10}^{30}}}\] \[\approx 0.0056\] \[\approx 0.01\] \[\approx {{10}^{-2}}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner