The value of acceleration due to gravity at Earth's surface is 9.8 ms⁻². The altitude above its surface at which the acceleration due to gravity decreases to 4.9 ms⁻², is close to (Radius of earth =6.4×10⁶ m )
A 9.0×10⁶ m
B 6.4×10⁶ m
C 1.6×10⁶ m
D 2.6×10⁶ m