So, given v, I have got a Y, given v dot I have got a Y, given v I have got also may be an
N depending on the direction and given v dot I have got an N. So, if I now plot this, v
against Y, v dash against Y and take the slope then I am getting getting this derivative,
because when I say Y v it is d y by d v. So, that means, that if there was an actually
velocity of v is my force would have been this into this, right because you see what we
are doing is that, this is my v, this is my Y, this is my slope here. So, this value is Y v
into v, because Y v is the slope, this is what the idea is