EnergyPart 6 - Power

…the rate at which energy is converted.

…the rate at which work is done.

…P

…measured in Watts (W), which is J/s.

Power is…

P = ΔE/t

P = W/t◦ But, W = FΔx, so P = FΔx/t◦ And Δx/t = v, so P = Fv

ΔE = change in energy t = time W = work F = force Δx = displacement v = velocity

Power Equations

Defined by James Watt:◦ The amount of work a horse can do in one

second.◦ One horsepower = 746 Watts

Horsepower

A 50.0 kg student climbs 5.00 m up a rope at a constant speed. if the student's power output is 200.0 W, how long does it take the student to climb the rope? How much work does he do?m=50 kgΔx=5 mP=200 Wt=?F=?W=?

F=mgF=(50)(9.8)F=490 N

P = FΔx/t

200t = (490*5)200t = (2450)

Pt = FΔx

t = (2450)/200t = 12.25 sW = FΔx

W = (490)(5)W = 2,450

J