Power work donetime requiredP FdtPFv550Energy, Work, and PowerPOWERRev. 0Page 9CP-05MechanicalPowerMechanical energy used per unit time is called mechanical power. Mechanical power is the rate atwhich work is done. Mechanical power is expressed in units of joules/sec (joules/s) or a watt (W)in the mks system, and feet - pounds force per second (ft-lbf/s) or horsepower (hp) in the Englishsystem. Mechanical power can be calculated using the following mathematical expression.Because work can be defined as force times distance, we can also use the following equation: (5-6)where:P=Power (W or ft-lbf/s)F=Force (N or lbf)d=distance (m or ft)t=time (sec)One horsepower is equivalent to 550 ft-lbf/s and 745.7 watts. Because in the equation above ddivided by tis the same as velocity, an alternate description of power is as follows.(5-7)where:P=power (hp)F=force (lbf)v=velocity (ft/s)When using equations 5-6 or 5-7, you must either assume force and velocity are constant or thataverage values of the force and velocity are used.

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