Question by Sarah: Please help me with these energy, power, and work concepts?
Are the following true or false
-Work can be done in the absence of motion.
-Without friction or work by an external force, the sum of the potential and kinetic energies of a body is constant.
-Energy conservation law for a projectile (no friction): Potential energy increase equals the kinetic energy decrease.
-Work is done when the form of energy changes.
-More power is required while slowly lifting a box than while lifting it up quickly.
-A source of energy is required to do work.
Answer by omnislash
1) False, work = force x distance traveled. Without motion, there is no distance traveled and so no work done.
2) True. As long as there is no external input of force or energy, the law of COE says that the sum of KE and PE and other forms of energy in that system remains a constant.
3) True. (same as above)
4) Work IS a form of energy. Not exactly true. In ideal cases, a form of energy can change to another, not necessary work.
5) True. Power is the rate of change of energy, If I can do the same work using a shorter time, I’m more powerful.
6) True. Some form of energy is required to convert to work because energy (work) CANNOT be CREATED from naught.
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