# HPhys5

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1. When does an object has energy
if it can produce a change in itself or in its surroundings.
2. Work
• is the product of the net force exerted on an object and the distance the object moves in the direction of the force.
•  W = Fd   N·m = Joule (J)
• If force is at an angle: W = Fd cos θ   (cos 90o = 0)
• Work is the transfer of energy by mechanical means. Energy is the ability to change an object.
3. Kinetic energy (KE):
energy an object has because of its motion.
4. Potential energy (PE):
energy an object has because of position, shape or form.
5. The net work done on an object is equal to its change in KE.
F = ma   W = Fx     W = max
6. Gravitational PE
• depends on the weight of the body and its separation from Earth.
• PE = mgh
7. How does PE depend on height?
• (Recall this equation:  vf2 = vi2 + 2gx and multiply each term by ½ m)
• E = ½ mvf2 = ½ mvi2 + mgh
• If h = 0, then E = ½ mv2
• If v = 0, then E = mgh
• Total E = KE + PE
• Note: need a reference level to calculate PE
8. Elastic potential energy
is energy available for use when a deformed elastic object returns to its original configuration.
9. The sum of KE + PE = mechanical energy.
10. the Law of Conservation of Energy
• According to the Law of Conservation of Energy, the total energy of a closed, isolated system is constant.
• (If something is conserved, we mean it remains constant.)
• Energy can change form but the total energy does not change.
• Note: mechanical energy is not conserved in the presence of friction.
11. Power
• is the rate of doing work or the rate at which energy is transferred.
• P = W/t        J/s = Watt (W)   P = Fd/t = Fv
 Author: doctorwhogirl998 ID: 189620 Card Set: HPhys5 Updated: 2012-12-15 17:39:46 Tags: Physics Folders: Description: Physics: Work and Energy Show Answers: