Question

why it is hard to climb stairs or hills

Answer 1

Because the higher we go, we lose our energy as potential energy. The higher we climb, we have to provide potential energy to carry our mass to the top.

Potential Energy, P = mgh. Where h is the height up to which we climb. m is the mass of our body. g is the acceleration due to gravity.

From the equation we can see that m is proportional to P. So, as mass increases, potential energy also increases. Therefore a person with more mass will lose more energy and find it difficult to climb hills or stairs than a thin person.

Answer 2

When you climb stairs or hills as it is not a plain level it will help your body to get exercised.