The height at which the value of acceleration due to gravity becomes 50% of that at the surface of the earth.(Radius of the earth =6400 km ) is

Acceleration due to graviy decreases by 50% means g'=g/2 g'=GM(R+h)2⇒g'=gR2R+h2=g1+hR2 ⇒g2=g1+hR2 ⇒2=1+hR2 ⇒2=1+hR ⇒hR=2-1=1.414-1=0.414 ⇒h=0.414×6400km=2649.6km