An object is dropped from an altitude of one earth radiusabove earth's surface. if m is the mass of earth and r is itsradius the speed of the object just before it hits earth isgiven by: a. √gm/r b. √gm/2r c. √2gm/r d. √gm/r2 e. √gm/2r2

The speed of the object just before it hits Earth is  

(A) is correct option.

Explanation:

Given that,

M = mass of earth

R = radius of earth

The potential energy at height above the surface of the earth

The kinetic energy at height above the surface of the earth

The total energy at height above the surface of the earth

....(I)

The total energy at the surface of the earth

....(II)

We need to calculate the speed of the object  just before it hits Earth

From equation (I) and (II)

Here, h = R

Hence, The speed of the object just before it hits Earth is  .

that would be because of both gravity and friction. so     c