Wally now lift the box of the floor and put it on a shelf. Does he doing any work? If not why? If so .what energy change is accurring?
To determine if Wally is doing any work, we need to understand the definition of work in physics. In physics, work is defined as the transfer of energy that results from the application of a force over a distance. Work is only considered to be done when both force and displacement occur in the same direction.
In this scenario, since Wally is lifting the box off the floor and placing it on a shelf, he is indeed doing work. This is because he is applying a force to lift the box against gravity, and the box is moving a distance in the vertical direction as it is lifted onto the shelf. Both the force and the displacement occur in the same direction.
The energy change that is occurring in this process is the conversion of Wally's chemical energy to mechanical energy. Wally's muscles are contracting, converting the chemical energy stored in his body into mechanical energy, which is then used to lift the box against gravity. As a result, the potential energy of the box increases, indicating an energy transfer from Wally to the box.
It's important to note that work is only done when there is a displacement in the direction of the force. If Wally holds the box without moving it or if the force and the displacement are perpendicular to each other, no work is done.