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# Alvl P1: work, energy and power (ch6) Cheat Sheet by MostAncientDream

aqa A-level physics Year 1(yr12) work, energy and power: chapter 6

### Work Done and Energy

 Work done is maximum when cos0 = 0 (the force and distance travelled are therefore parallel) Work done is minimum when cos0 = 90 (the force and distance travelled are therefore perpen­dic­ular) types of energy: - kinetic energy - potential energy - thermal energy (not covered in this spec point) for example: a ball held at a height will have Ep, when dropped and landing on the ground (assuming there is no energy loss) all the energy will be converted into Ek. Δ E = W --> change in energy in a system = work done on a system

### Derriv­ations

 Gravit­ational Potential Energy: ΔE = W ΔE = Fxcos0 (work done is force x distance x angle) where F = ma (in this case a is g) and distance is hieght travelled ΔE = mghcos0 as cos0 where 0 is 0' cos0 = 1 so ΔE = mgh Kinetic Energy: ΔE = W ΔE = Fxcos0 (work done is force x distance x angle) ΔE = Fs (cos0 = 1) ΔE = mas as v2 = u2 + 2as rearrange where u = 0 as = v2/2 therefore ΔE = 1/2 mv2

### Defini­tions

 Work done product of the force and the distance moved in this direction power rate of work done rate of energy transf­erred

### Equations

 Work done Fxcos0 ---(where x is distance and 0 is theta between f and x) change in energy ΔE = W power W/t Fx/t Fv efficiency useful­/total (x100)

### Conversion of energy

 example of findign resistive forces going down hill --top | v=0 ------| -------| --------| --bottom | v=8 a ball is roll down from the top to the bottom -length of the ramp is 7m -height is 5m as ΔE = W energy at top (Ep no Ek) then energy at bottom (Ek no Ep) from this we know it is all transf­erred (assuming no loss to heat) therefore ΔE = mgh - 1/2mv2 mgh - 1/2mv2 = Fx (where x is length of ramp) then just put in numbers to solve for F

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