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Introductory Physics Homework Help
The Work Done on a Sliding Box: How to Calculate Friction and Applied Force
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[QUOTE="murrskeez, post: 4535721, member: 446090"] [h2]Homework Statement [/h2] A box of mass m is sliding along a horizontal surface. Part A) The box leaves position x=0 with a speed v[SUB]0[/SUB]. The box is slowed by a constant frictional force until it comes to rest at a position x=x[SUB]1[/SUB]. Find F[SUB]f[/SUB], the magnitude of the average frictional force that acts on the box. (express in terms of m, v[SUB]0[/SUB], and x[SUB]1[/SUB]. I found the correct answer to part A...(F[SUB]f[/SUB]=(mv[SUB]0[/SUB][SUP]2[/SUP])/2x[SUB]1[/SUB]) Part B) After the box comes to rest at a position x[SUB]1[/SUB], a person starts pushing the box giving it a speed v[SUB]1[/SUB]. When the box reaches position x[SUB]2[/SUB] (where x[SUB]2[/SUB]>x[SUB]1[/SUB]), how much work W[SUB]p[/SUB] has the person done on the box? Assume that the box reaches x[SUB]2[/SUB] after a person has accelerated it from rest to speed v[SUB]1[/SUB]. Express the work in terms of m,v[SUB]0[/SUB],x[SUB]1[/SUB],x[SUB]2[/SUB], and v[SUB]1[/SUB]. [h2]Homework Equations[/h2] W=ΔKE W=F*d[h2]The Attempt at a Solution[/h2] So I figured that the total work would be the work done in part A (-(mv[SUB]0[/SUB][SUP]2[/SUP])/2x[SUB]1[/SUB])*(x[SUB]1[/SUB]) added to the work done between x[SUB]1[/SUB] and x[SUB]2[/SUB]: -(mv[SUB]0[/SUB][SUP]2[/SUP](x[SUB]2[/SUB]-x[SUB]1[/SUB]))/2x[SUB]1[/SUB] however when I add these two solutions, it tells me that the answer needs to include v[SUB]1[/SUB]. So then I thought to solve for v[SUB]1[/SUB] by setting the work done between x[SUB]1[/SUB] and x[SUB]2[/SUB] equal to the change in kinetic energy between that time frame which gave me: KE = (mv[SUB]1[/SUB][SUP]2[/SUP])/2 = work between x[SUB]1[/SUB] and x[SUB]2[/SUB] v[SUB]0[/SUB][SUP]2[/SUP]=(x[SUB]1[/SUB]v[SUB]1[/SUB][SUP]2[/SUP])/-(x[SUB]2[/SUB]-x[SUB]1[/SUB]) so that allowed me to have v[SUB]1[/SUB] in my final answer...but mastering physics is still telling me it's incorrect. Any advice/help would be great. [/QUOTE]
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The Work Done on a Sliding Box: How to Calculate Friction and Applied Force
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