a 500 kg mass with a static coefficient of 0.55 and a kinetic coefficient of 0.50 is to be dragged along a floor.what horizontal force is needed to start the mass moving?

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Since you are asked to find the force needed to start the mass moving you take the static coefficient first.The frictional force=F normal*static coefficient=5000*.55=2750N ( since the box is on the floor, the normal force=Fgravity=5000N) You need 2750N to start the mass moving , then you may need only 2500N ( you use kinetic friction , once it starts moving)