Final answer:
When a man in a gym lifts a weight and puts it down in the same position, no work is done by the man or the gravitational force. However, energy is still expended by the man's muscles. The amount of energy spent cannot be quantified based solely on the mass and height, and the energy expenditure is dependent on the time taken for the action.
Step-by-step explanation:
When a man in a gym lifts a weight and then puts it down where it was before, the work done by the man to the weight is zero. This is because work is defined as the force applied to an object multiplied by the distance the object moves in the direction of the force.
In this case, the man applies a force to the weight, but the weight does not move in the direction of the force since it is put down in the same position.
The work done by the gravitational force on the weight is also zero. This is because the weight is not moved vertically against gravity when it is put down in the same position.
The amount of physical energy spent by the man for this physical performance is not zero. Even though the work done is zero, the muscles in the man's body still require energy to contract and lift the weight. However, we cannot quantify this energy based solely on the mass and height. Other factors, such as the efficiency of the man's muscles, also play a role.
The energy spent by the man is not independent of the time used for this action. If the man lifts the weight quickly, more power is required, and therefore more energy is spent. If the man lifts the weight slowly, less power is required, and therefore less energy is spent.