Peoples Physics Book Version-2

http://www.ck12.org Chapter 9. Energy and Force Version 2

9.4 Summary of Key Equations and Definitions

Here is a summary of important concepts from this and the past few chapters. The point of this chapter is to combine
all of our knowledge so far to solve new kinds of problems.

Transfers

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W=F·d Work is the dot product of force and displacement

P=∆∆Et Power is the rate of change of energy of a system,in Watts(J/s)

J= p=F∆t Impulse is the change in a system′s momentum

Conservation Laws

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∑pinitial=∑pfinal Total momentum is constant in closed systems

∑Einitial=∑Ef inal Total energy is constant in closed systems

∑Kinitial=∑Kf inal Kinetic energy conservedonlyin elastic collisions

One important type of problem is called acollisionproblem. In cases where collisions are elastic, kinetic energy
and momentum are conserved. In inelastic collisions, only momentum is conserved.