Coefficient of kinetic friction between box and floor

  • #1

Homework Statement


A 98 N box of oranges is being pushed across a horizontal clean steel surface until it stops. As it moves, it is slowing down at a constant rate of 1.1m/s each second. The push force has a horizontal component of 25N and a vertical component of 20N downward. Calculate the coefficient of kinetic friction between the box and the floor.


Homework Equations





The Attempt at a Solution


summation of Fx = 25N - fk = ma
= 25N - fk = (10kg)(1.1m/s^2)
fk = 14N???
summation of Fy= 0 = -Fw - Fdown +normal force
normal force = 20N + 98N = 118N???

fk = (uk)(Fn)
(14N / 118N) = uk
uk = 0.119
 

Answers and Replies

  • #2
PhanthomJay
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You're on the right track, but not quite there yet. The box is slowing down. What's the direction of the acceleration and the net horizontal force acting on the box?
 
  • #3
thanks phantomjay
summation of Fx = 25N - fk = ma
= 25N - fk = (10kg)(-1.1m/s^2)
fk = (1.1m/s^2)(10kg) +25N
fk = 36N

uk = (36N/118N)
uk = 0.305

is this right?
 
  • #4
PhanthomJay
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Yep, looks real good now, although you should round off the uk value to 0.3. Nice work.
 
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