Question

The energy required to remove a body of mass m from earth’s surface is/are equal to

• A. 2mgR
• B. mgR
• C. –mgR
• D. Zero

Answer 1

Answer: (B)

mgR

Answer 2

The potential energy of the body on the surface of each = U₁ = - $\frac { \mathrm { GMm } } { \mathrm { R } }$ . The potential energy of the body in the surface at infinity U₂ = 0

⇒ ∆U = U₂-U₁ = $\frac { \mathrm { GMm } } { \mathrm { R } } = \operatorname { mgR } \left( \because \mathrm { g } = \frac { \mathrm { GMm } } { \mathrm { R } ^ { 2 } } \right)$

Therefore (2).