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Laws of Energy
Engineering 10
San Jose State University
Power in terms of physical quantities
Sourcing Energy
Energy conversion
Receiving Energy
Force, Speed, Voltage, Current, etc.
The rate of energy conversion or transmission (i.e. power) is related to the physical quantities such as force, speed, voltage, current, etc.
(c) P.Hsu 2009
Force Speed (Newton) (m/s)
For mechanical system, rate of energy transfer (i.e., power) to an object is the product of the force (F in Newton) and the speed (S in meter/sec) of the point where the force is applied.
Power = F x S (c) P.Hsu 2009
Q1. A person pushes an out-of-gas car with a force of 100 Newton (about 22.5 lb of force) to maintain a speed of 0.2 m/s. It took him 10 minutes to get to the nearest gas station. How much energy did this person use to do this work?
(Hint: Power = Force x Speed)
(A) 20 J (B) 600 J (C)1200 J (D) 2400 J
(E) 12000 J
(c) P.Hsu 2009
• Energy = Power x Time
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