Conservation of Energy & FrictionConsider a block that is given an initial velocity Voon a horizontal surface where μ= μk. The block comes to a stop due to the frictional force acting on it. Let’s define the isolated system to be the block + surface. sMMvovf= 0system = block + surfaceRecall that the work done by all the external forces acting on a system is given by: (1) extmechsyssysWEKU= ∆= ∆+ ∆Because0extW=( there are NOexternal forces acting on the system) and ∆Usys= 0, then this implies that ∆Ksys= 0. However we know that 212sysoKMv∆= −. Since we have an isolated system there is no transfer of energy into or out of system and since energy cannot be created or destroyed, where did the decrease in energy (kinetic) of the system go? The decrease in energy (kinetic) of the system
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