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Physics ramp/acceleration problem!

  1. Nov 9, 2012 #1
    Block A has a mass of 5.26 kg and is on a rough incline of 16.0°to the horizontal. Block B has a mass of 4.80 kg and the coefficient of kinetic friction between Block A and the plane is 0.204. What is the acceleration of the blocks?

    Equations= fnet=ma

    Attempt:(4.8+5.26)a=(4.8)g-(5.26)gsin(16°)-(μ)(9.8)(5.26)(cos(16°))
    Therefore a=3.00m/s^2
    This comes out to be the wrong answer, according to the key. Help?!
     
  2. jcsd
  3. Nov 9, 2012 #2
    I get 1.7 m/s^2. Tell me if thats right and i will explain.
    i think you went wrong on the friction bit. Friction = UN and force N=FG. You didn't add all your masses for some reason on the friction part.
     
  4. Nov 9, 2012 #3
    Nope, unfortunately they say that's wrong D:
     
  5. Nov 9, 2012 #4
    I see what i did XD
    Lets see.... (If this isn't right, ill shoot myself...JK)


    Sum of F = ma
    Fg - Ff = ma
    mg - UN = ma
    m1+m2gsin(16) - U X m1+m2cos(16)=m1+m2(a)
    a= m1+m2gsin(16) - Ux m1+m2cos(16)/ m1+m2
    a= 5.26+4.8sin(16) - 0.204 X 5.26+2.8cos(16)/ 5.26+2.8
    a=-1.84
     
  6. Nov 9, 2012 #5
    a = -1.84 m/s^2 :P
     
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