Question

A body of mass 100 kg falls on the earth from infinity. What will be its velocity on reaching the earth? What will be its K.E.? Radius of the earth is 6400 km and g = 9.8 $ms^{-2}$. Air friction is negligible.

Answer 1

The Kinetic energy of the body is 6.27 x 10^9 J.

Explanation:

u  i +k  i  =u  f   +k f

⇒ 0 + 0 =  R  − GMm / R +  1/2 mv^ 2

1/2 mv^ 2  = GMm  / R x R

=> mgR

= 100 x 9.8 x 6400 x 1000

= 6272000 x 100

= 6.27 x 10^9 J

Hence the Kinetic energy of the body is 6.27 x 10^9 J.

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