Question

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

• A. $\sqrt{g R}$
• B. $2 \sqrt{g R}$
• C. $\sqrt{2 g R}$
• D. $\sqrt{\frac{g R}{2}}$

Answer 1

Answer: (A)

$\sqrt{g R}$

Answer 2

The correct answer is (A) : $\sqrt{g R}$
Loss in PE = Gain in KE
(−2RGMm​)−(−RGMm​)=21​mv2
⇒v2=RGM​=gR
⇒v=gR​