Question

A body is fired from surface of earth. It goes to
maximum height equal to radius of earth, from earth
surface. The initial speed given is

a)7.95 km/s
b)5.45 km/s
c)9.81 km/s
d)11.2 km/s​

Answer 1

Explanation:

g=

R

2

GM

e

Applying law of conservation of mechanical energy:-

2

1

mu

2

−

R

GM

e

m

=−

R+h

GM

e

m

⟹

2

u

2

−gR=

R+h

−gR

2

⟹

R+h

gR

2

=

2

2gR−u

2

⟹R+h=

2gR−u

2

2gR

2

⟹h=

2gR−u

2

2gR

2

−R

⟹h=

2gR−u

2

u

2

R