KVPY Sample Paper KVPY Stream-SX Model Paper-27

  • question_answer
    Suppose Earth's orbital motion around the Sun is suddenly stopped. What time will the Earth take to fall into the Sun?

    A) 2 months

    B) 2 years

    C) 2 days

    D) 20 days

    Correct Answer: A

    Solution :

    When the Earth's motion is suddenly stopped, it would fall into the Sun and (suppose) it comes back. If the effect of temperature of Sun is ignored, we can say that the Earth would continue to move along a strongly extended flat ellipse whose extreme points are located at the Earth's orbit and at the centre of the Sun.
    The semi major axis of such ellipse is \[R/2.\]
    Now \[\frac{{{T}^{'2}}}{{{T}^{2}}}={{\left[ \frac{R}{2} \right]}^{3}}\left[ \frac{1}{{{R}^{3}}} \right]\]
    Where 7'is the time period of normal orbit of
    Earth,
    Or \[T{{'}^{2}}=\frac{{{T}^{2}}}{8}\operatorname{or}\,T'=\frac{T}{2\sqrt{2}}\]
    Now, time required to fall into the Sun,
    \[t=\frac{T'}{2}=\frac{T}{4\sqrt{2}}=\frac{365}{4\sqrt{2}}\approx 65\operatorname{days}\]
    So, the Earth would take slightly more than 2 months to fall into the Sun.


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