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Acceleration on an Inclined Plane?

  • Thread starter haengbon
  • Start date
  • #1
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Homework Statement



A box weighing 20 kg is on an inclined plane with an angle of 30[tex]\circ[/tex].The coefficient of friction is 0.3. What is the acceleration of the box?


Homework Equations



Newton's Second law ( I think? )

g= 10 m/s2

The Attempt at a Solution




[tex]\sum[/tex]y = 0
NF - Wysin30[tex]\circ[/tex] = 0
NF = Wysin30[tex]\circ[/tex]
NF = [(20)(10)]sin30[tex]\circ[/tex]
NF = 100 N

f = [tex]\mu[/tex]NF
f = (0.3)(100)
f = 30

[tex]\sum[/tex]x = ma

Wcos30[tex]\circ[/tex] + f = m(-a)
20cos30[tex]\circ[/tex] + 30 = -20a
[tex]47.32/-20[/tex] = [tex]-20a/-20[/tex]
a = -2.36 m/s2

Is this correct? :D
 

Answers and Replies

  • #2
ideasrule
Homework Helper
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You have your sines and cosines mixed up. The normal force is Wcos(theta); the parallel force is Wsin(theta).
 
  • #3
38
0
You have your sines and cosines mixed up. The normal force is Wcos(theta); the parallel force is Wsin(theta).
so that's the only problem ? :D so If I switched/corrected the two, then my answer would immediately be correct? :D
 

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