 # sir please explain me the energy diagrams for potential energy.....and i have a doubt regarding potential energy and kinetic energy that if a body is at rest then which energy does it contain ....Potential Energy or Kinetic Energy ???because if we take the axis at which body is placed to be potential energy as 0 then which energy we should take in it ??? Puneet Mittal AskiitiansExpert-IITD
22 Points
12 years ago

Hi Ankit,

The potential energy of a body depends on mass of body , mass of earth and distance of body from the centre of earth.

It is given by the formula : -GMm/R

Now when we calculate potential and kinetic energy we are referring to changes in potential energy from starting position to final position. for example if a body moves from height 0 to h then its energy changes from -GMm/R to -GMm/(R + h)

using g = GM/R2 , change in potential energy is from -mgR  to -mgR2/(R+ h)...Difference will give -mgR( R + h - R )/(R + h)

or change will be -mghR/(R + h), For small h, change will be -mgh which we usually write in our equations.

Now , If a body is at rest then it has potenital energy in it. Since it has no speed so it has zero kinetic energy.

The value of that energy is -GMm/R

Now , if you take axis at which body is placed to be potential energy as 0 then both potenitial energy and kinetic energy will be zero because we have chosen th is point to have zero potential energy.We do this as we are Interested only in changes in potential energy ( mgh ).

We can take -GMm/R , the position at which body is kept on earth, to be potenital energy as zero to make our calculations easy.

Please feel free to ask as many questions you have.

Puneet