JEE Main & Advanced Physics Gravitation / गुरुत्वाकर्षण Question Bank Critical Thinking

  • question_answer
    A projectile is projected with velocity \[k{{v}_{e}}\] in vertically upward direction from the ground into the space. (\[{{v}_{e}}\] is escape velocity and \[k<1)\]. If air resistance is considered to be negligible then the maximum height from the centre of earth to which it can go, will be : (R = radius of earth) [Roorkee 1999; RPET 1999]

    A)             \[\frac{R}{{{k}^{2}}+1}\]

    B)             \[\frac{R}{{{k}^{2}}-1}\]

    C)             \[\frac{R}{1-{{k}^{2}}}\]  

    D)             \[\frac{R}{k+1}\]

    Correct Answer: C

    Solution :

                    Kinetic energy = Potential energy             \[\frac{1}{2}m\,{{(k{{v}_{e}})}^{2}}=\frac{mgh}{1+\frac{h}{R}}\]Þ \[\frac{1}{2}m{{k}^{2}}2gR=\frac{mgh}{1+\frac{h}{R}}\]             \[\Rightarrow \,h=\frac{R{{k}^{2}}}{1-{{k}^{2}}}\] Height of Projectile from the earth's surface = h Height from the centre \[r=R+h=R+\frac{R{{k}^{2}}}{1-{{k}^{2}}}\] By solving \[r=\frac{R}{1-{{k}^{2}}}\]


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