Which of the following statements is/are true? Explainastion required 1. The tot
ID: 2238534 • Letter: W
Question
Which of the following statements is/are true? Explainastion required 1. The total mechanical energy of a system is equally divided between kinetic and potential energy. 2. The total mechanical energy of a system is constant only if nonconservative forces act. 3. Mechanical energy can be dissipated to nonmechanical forms of energy. 4.The total mechanical energy of a system, at any one instant, is either all kinetic or all potential energy. 5. The total mechanical energy of a system is constant only if conservative forces act.Explanation / Answer
The total mechanical energy of a system...
a. is constant, only if conservative forces act.
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A conservative force is any force for which we track an associated potential energy, contributing to the total mechanical energy.
The following are conservative forces:
Gravity
Electrostatics
Elastic forces, as in springs
The following are forces of constraint and do zero work.
Tension in an inextensible string
Normal force of contact for a rigid surface
Static friction
The following forces are non-conservative:
Sliding friction
Air drag
Human forces (pushes and pulls)
With elastic forces, gravity, and electrostatics, we have an associated potential energy for all of them. The combination of all potential energies and the KE of the system is conserved when only these forces act.
Normal forces of constraint act perpendicular to motion, or have no relative motion. For this reason, these forces do not alter the total mechanical energy.
Friction and air drag convert mechanical energy into heat. We might be interested in mathematically tracking this heat, but we cannot convert it back to mechanical energy. For human forces, we also cannot easily convert the work done by humans back to food energy when we use our muscles to lower a box to the ground. Therefore, human forces are considered non-conservative.
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