A particle of mass ‘m’ is kept at rest at a height 3R from the surface of earth, where ‘R’ is radius of earth and ‘M’ is mass of earth. The minimum speed with which it should be projected, so that it does not return back, is( g is acceleration due to gravity on the surface of earth)

Options

(a) (GM / R)¹/²
(b) (GM / 2R)¹/²
(c) (GR / 4)¹/²
(d) (2G / 4)¹/²

Correct Answer:

(GM / 2R)¹/²

Explanation:

As we know, the minimum speed with which a body is projected so that it doe snot return back is called escape speed.
vₑ = √(2GM / r) = √(2GM / R + h) = √(2GM / 4R)
= (GM / 2R)¹/² ( h = 3R)