Peoples Physics Concepts

8.5 Energy Problem Solving

8.5 Energy Problem Solving

• Analyze and solve more complicated problems involving energy conservation.

Students will learn how to analyze and solve more complicated problems involving energy conservation.

Key Equations

∑Einitial=∑E

final ;T hetotalenergydoesnotchangeinclosedsystems

KE=^12 mv^2 ; Kinetic energy

PEg=mgh; Potential energy of gravity

PEs p=^12 kx^2 ; Potential energy of a spring

W=Fx∆x=F dcosθ; Work is equal to the distance multiplied by the component of the force in the direction it is

moving.

Guidance

The main thing to always keep prescient in your mind is that the total energy before must equal the total energy after.

If some energy has transferred out of or into the system via work, you calculate that work done and include it in the

energy sum equation. Generally work done by friction is listed on the ’after’ side and work put into the system, via

a jet pack for example, goes on the ’before’ side. Another important point is that on turns or going over hills or in

rollercoaster loops, one must include the centripetal motion equations -for example to insure that you have enough

speed to make the loop.

Example 1

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/353

Watch this Explanation