A simple application Work done by gravity on a falling object What is the speed of an object after falling a distance H, assuming it starts at rest? Wg=mg△rcos(0)=mH 0 Wo= mgH H/rmg Work Kinetic-Energy Theorem: Wa=mgH= 12mv2 ugH Physics 121: Lecture 12, Pg 16
Physics 121: Lecture 12, Pg 16 A simple application: Work done by gravity on a falling object What is the speed of an object after falling a distance H, assuming it starts at rest ? Wg = mg r cos(0) = mgH Wg = mgH Work Kinetic-Energy Theorem: Wg = mgH = 1 /2mv2 r mg H j v0 = 0 v v = 2gH
What about a sum of forces? Suppose For=F,+ F2 and the displacement is△r. The work done by each force is TOT 1=F1cosb,△r,and △ W2=Fcos2△r WTOT=W1+ W2 Wror= FToCOS6△r It's the total force that matters ! Physics 121: Lecture 12, Pg 17
Physics 121: Lecture 12, Pg 17 What about a sum of forces? Suppose FTOT = F1 + F2 and the displacement is r. The work done by each force is: W1 = F1 cos 1 r , and W2 = F2 cos 2 r WTOT = W1 + W2 WTOT = FTOTcos r It’s the total force that matters !! FTOT r F1 F2 1 2