An object is allowed to fall from a height R above the earth, where R is the radius of earth. Its velocity when it strikes the earth’s surface, ignoring air resistance, will be:
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An object is allowed to fall from a height R above the earth, where R is the radius of earth. Its velocity when it strikes the earth’s surface, ignoring air resistance, will be:

G1 Physics · Accepted Answer

Initial distance from Earth’s centre is 2R. By energy conservation: GMm/R − GMm/(2R) = (1/2)mv². Thus v² = GM/R = gR, so v = √(gR).