# (a) A book has a mass 400 g. Find its weight when taken from the surface to a height equal to the radius of the earth.(b) Define weight.

(a) Given,
mass of book(m)=400 g=0.4 kg
Let the radius of the earth be R.
height of book=R
the distance of book from the centre of the earth(d)=radius of earth + height of book=R+R=2R
The acceleration due to gravity at the surface of the earth(g) is given by,
The acceleration due to gravity at such height(g’) is given by,

Weight(W’)=mg’=0.4×2.45=0.98 N

(b) Weight is the force with which a body is attracted towards the center of the earth. It is directly proportional to the acceleration due to gravity. It is given by, Weight=mass × acceleration due to gravity

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