Question

Find the weight of an object at a height of 6400 km above the
earth’s surface. The weight of the object

at
the surface of the earth is 20 N and the radius of the earth is 6,400 km. 

Plz answr this fast i need the answer to this question today itself.....plz fast....

Answer 1

F = GMm
         R² 
M is the mass of the Earth m is the mass of the object 
R is the radius of the earth =6400km(given)

When object is kept on surface.
W=F=GMm= 20 N
            R²
 When object is lifted to a certain height=R' = R+h = 2R
 h = R = 6400 km
Now we have weight of  the object is

W' = F' =  GMm
                (2R)² 
W' = (1/4).(GMm)
                    R² 
=W
  4
Now the weight of the object will be
weight=20
             4
W=5N

Answer 2

The weight of a object at the surface of the earth is 20N and radius of the earth is 6400 km.

We have to find the weight of the object at a height 6400 km above the earth's surface.

Weight of an object at a height h above the earth's surface is given by,

$W=\frac{W_0}{\left(1+\frac{h}{r}\right)^2}$

where W₀ is the weight of the object at the surface of the earth and r is the radius of earth.

here, W₀ = 20 N , r = 6400 km , h = 6400 km

∴ W = 20/[1 + (6400/6400)]²

= 20/(1 + 1)²

= 20/4

= 5 N

Therefore the weight of object at a height 6400 km above the earth's surface is 5N.