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AP Unit I C 4 Power. 4. Students should understand the definition of power, so they can:
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4. Students should understand the definition of power, so they can: • A) Calculate the power required to maintain the motion of an object with constant acceleration(e.g., to move an object along a level surface, to raise an object at a constant rate, or to overcome friction for an object that is moving at constant speed).
B) Calculate the work performed by a force that supplies constant power, or the average power supplied by a force that performs a specified amount of work.
Power • Power is the rate of doing work. • Power = Work Done/ TimeTaken • P = W/t or P avg = W / Δt • Power is measured in Joules per second or Watts ( J/s or W)
Power and Velocity • Since P = W/t and W = F d cos θ then • P = (F d cos θ)/t • Since d/t = v then • P = F v cos θ
Power Calculations • 1. A crane lifts a mass of 555 kg at 2.5 m/s. Calculate (a) power and (b) tension in rope. • If it rises to a height of 25 meters, calculate time taken and work done. • 2. If the rope snaps, with what speed will it hit the ground. • If it penetrates to a depth of 0.25 meters calculate the force exerted by the ground on the block.