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JEE Advanced 2015Paper 1
Exam
JEE Advanced
Year
2015
Paper
Paper 1
Subject
Physics
Chapter
Gravitation

JEE Advanced 2015 · Paper 1 · Physics · Gravitation

A bullet is fired vertically upwards with velocity υ from the...

A bullet is fired vertically upwards with velocity υυ from the surface of a spherical planet. When it reaches its maximum height, its acceleration due to the planet's gravity is 14th\dfrac{1}{{4}^{th}} of its value at the surface of the planet. If the escape velocity from the planet is υesc=υN{υ}_{esc} = υ\sqrt{N} , then the value of N is (ignore energy loss due to atmosphere)A bullet is fired vertically upwards with velocity υ from the surface of a spherical planet. When it reaches its

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A bullet is fired vertically upwards with velocity υ from the surface of a spherical planet. When it reaches its
g′=g(1+hR)2=g4{g}^{′} = \dfrac{g}{{\left(1 + \dfrac{h}{R}\right)}^{2}} = \dfrac{g}{4}
1+hR=21 + \dfrac{h}{R} = 2
h=Rh = R ...(i)
So velocity of particle becomes zero at h=Rh = R
Given vesc=vN{v}_{esc} = v\sqrt{N}
So 2GMR=vN\sqrt{\dfrac{2GM}{R}} = v\sqrt{N} ...(ii)
Applying conservation of energy
−GMmR+12mv2=−GMm2R+0\dfrac{- GMm}{R} + \dfrac{1}{2}m{v}^{2} = - \dfrac{GMm}{2R} + 0
On solving
v2=GMR{v}^{2} = \dfrac{GM}{R}
So v=GMRv = \sqrt{\dfrac{GM}{R}} putting in equation (ii)
2GMR=vN\sqrt{\dfrac{2GM}{R}} = v\sqrt{N}
Comparing N=2N = 2
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