A projectile is fired upward from the surface of the earth with a velocity kve, where ve is escape velocity and k<1. If R is the radius of earth, then neglecting the air resistance, the maximum height to which it will rise is
A
kR2−k2
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B
RR2−k2
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C
k1−R2
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D
k2R1−k2
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Solution
The correct option is Dk2R1−k2 If a body is projected from the surface of earth with a velocity v and reaches a height h, then by conservation of energy (relative to surface of earth) 12mv2=mgh[1+(hR)] In this case, v=kve=k√2gR So, 12k2(2gR)=gh[1+(hR)]ork2=hR+h ork2R+k2h=h⇒h=k2R1−k2