Question

A man weighs 50 kg at the Earth's surface. At what height above the Earth's surface does his weight become 25 kg?

Answer 1

First thing kg isn't the unit of weight, newton is. Kg is the unit of mass.

First you need to calculate the mass of man.

You know, W=mg

So m=W1/g, W1=50N.

Mass never changes. Reduction in weight is due to lack of gravity.

So let at h height man's weight becomes 25N, and at that height gravity is g’.

As you know mass never changes so at that height mass would be same.

So you can calculate g’

g’=W2/m, where W2=25N.

Now you have gravity at that height. You need to calculate the height.

g’=g(R/R+h)^2

Where R=radius of Earth. R=6.4*10^6m.

And g is gravity on earth surface, g=9.81m/s2.

So with that formula you can easily calculate the height.