- #1
cleverfield
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Homework Statement
Two masses M1 = 2.5kg and M2 = 4.0kg are on inclines and are connected together by a string . The coefficient of kinetic friction between each mass and its incline is Uk = 0.30.
If moves up, and moves down, determine their acceleration.
Homework Equations
The Attempt at a Solution
M1:
F=ma
x:T-0.30N-(2.5)(9.8)SIN51 = 2.5a
y:N-(2.5)(9.8)cos51=0
N=(2.5)(9.8)cos51
T - 0.30((2.5)(9.8)cos51) - (2.5)(9.8)sin51 = 2.5a
T= 2.5a + 0.30((2.5)(9.8)cos51) + (2.5)(9.8)sin51
M2:
x: (4.0)(9.8)sin21 - T - 0.30N = 4.0a
y: N-(4.0)(9.8)cos21 = 0
(4.0)(9.8)sin21 - T - 0.30((4.0)(9.8)cos21) = 4.0a
-T = 4.0a - (4.0)(9.8)sin21 + 0.30((4.0)(9.8)cos21)
T = -4.0a + (4.0)(9.8)sin21 - 0.30((4.0)(9.8)cos21)
therefore
2.5a + 0.30(m1gcos51) + m1gsin51 = -4.0a + m2gsin21 - 0.30(m2gcos21)
6.0a = -0.30((2.5)(9.8)cos51) - (2.5)(9.8)sin51 + (4.0)(9.8)sin21 - 0.30((4.0)(9.8)cos21)
a = -0.31
This answer is negative and I think it should be positive, but I am not even sure if I have taken the appropriate steps.
Thanks for any help!