A body is projected vertically upwards from the surface of earth with a velocity sufficient enough to carry…

A body is projected vertically upwards from the surface of earth with a velocity sufficient enough to carry it to infinity. The time taken by it to reach height h is           S.

  1. Re2 g1+hRe32-1
  2. 2Reg1+hRe32-1
  3. 13Re2 g1+hRc32-1
  4. 132Rcg1+hRe32-1

Solution

Applying energy conservation from (1 to 2,
12 m·2GMRe-GMmRe=12 mv2-GMmR+r

12mv2=GMmR+r

v=2GMR+r=drdt

 2GM0tdt=ReRe+h(R+r)dr

2GM·t=23(R+r)32ReRe+h

t=23Re32GM1+hRe32-1

GMRe2=g

t=132Re g1+hRe32-1

Asked in: JEE Main 2021 (22 Jul Shift 1)

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