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WORK - ENERGY + POWER Work + defined as a constant force applied onto an object at an angie @ over a displacement dz. W =: FAxcosO where: W: Work CT) F = force CN) AX = Displacement cm) 8 = Angle bin the force 2 displacement: € in ‘this section, you will need to be able to: ') Draw FRO 2) Calculate net work done on an object 3) Distinguish b/n tve and -v@ work done on a system. we can use 2 formulae for W = ) @ W= FAx cos 6 oR Wet = FEnet Ax cose # the difference bln these 2 formulae is that (0) applies to a sing luac force whereas (2) applies to the total fores- * there are 2 methods to Solve for net work done. S You will know how to use both, but you will Usa method 2 on! { Created with | J Notewise Method One : a) draw FBO of all faces acting on the object - b) derermine @ bln each Force and the direction of motion] displacement. C) USC W= FAxtose to determine the work done by tach force. d) calc. the sum of the Net work done by all the forces «© Wnhet = WitWet Wat--.t Wa Method two: a) draw FBD of all the forces aching along the plane of mobon. b) (9nore the forces that act parperdicular to the plane, because they, do Zero work on the object U why? > L means @= 490° > Cosl40) = o math W: FAxcos4o perspective W > Fax (0) Cxplaination + when a force is W= 0 applied onto an object, the object will move in the x-direction; C) Caledlate the net force — aCCeleration and velocity just works or Sum of forces in the \ke that, unless the object is 7] plane. oriented in the y-direction. So if Fnet= Fit Fot--t En the object moves in the x-direction, and does not move in the y-direction, then 2eFr0 work {$ Qs: ise Work-Energy Theoram ~ the net work done on an object IS equal to the change in the object's Kinetic energy. Wnet= AEk Whet = Ef - Ec Ww \ tmuyt nek = Zz Muft - ZT My Lo literally when @= 90° Conservative force 1 - q force iS a Conservahve force if : the net work done by the force is tero while moving the objet Around a Closed Path, Starting, Ond ending at the Same point: Ls if a conservahye force is the only force aching on On object during ts mohon, the mechanical erg dF the object 1s conserved. ~ examples of 4 Consetvative force: gravitational force and electvostahc force - if you're sill confused, think about it like this : Fu let's Say we have an Object Where there's a ff oe > fapp force applied , there's a notmal force and "9 gravitation Fae wise we Said that whan solving for Waet, we exclude the perpendicular forces because the angles are @=40° And Cos 40 = 0. Al the forces that do no work Cand are basically Chilling) , they are Conservative forces. Non- conservative forces - a force fs non-consewative force if the wofk done by the force Causes a Change in the Sum of the grautahonal Potential energy and the kinetic energy, and thus, to the mechonical energy of the object - examples: frictional force; air resistance ; an applied force, or tension force - ¥ Mote + work done by all non-conservahve Porees i$ equal to the change in the total mechanical erg of the Object: Waonconservative 8 OEp + Ek Powar : Ww p> At Lo the rate at which work is done or enegy Is expended. Created with Notewise 3) A Car with a mass of 600 kq accelerates from lom-s' to So ms' in 25S on @ horizontal firchintess aurface- Calculate the Car's power. '" \) < a Oy Wet aat lot a (25) Vi = ioms! 4o = 254 V4 = bomS' 25 2S ot = 25s. a= oS x \ NO r C-2] im) w lo ms? Fema F = (Soo)LI-6) F = S00N V4t= Wi2t 2anx W= Faxcose BO2= 10% + 2( 1b) 2% = (800 )(150) cos (0) 2500 = 100+ 3.25% = 600 000T 200 = 3-24x Aw = 750m 600 0900 2 Ps 78S P= 2h 000W or 24 kW Created with Notewise 
