Two blocks attached by a string slide down a 17 incline. The lower block has a mass of 0.2 kg and a coefficient of kinetic friction of 0.2. The upper block has a mass of 0.9 kg and a coefficient of kinetic friction of 0.9. Find the magnitude of the acceleration of the blocks. The acceleration of gravity is 9.81 m/s2 .
uk = kinetic coefficient
Fx1 = m1a = m1gsin 17 - T - uk1 * m1gcos 17
Fx2 = m2a = m2gsin 17 + T - uk2 * m2gcos17
The Attempt at a Solution
a(m1+m2) = (m1 + m2)gsin 17 - uk1 * m1gcos 17 - uk2 * m2gcos 17
a = -4.3765924 m/s^2
However, the answer was a = 4.3765924 m/s^2.
It seems like the equation was:
Fx1 = m1a = T + uk1 * m1gcos 17 - m1gsin 17
Fx2 = m2a = uk2 * m2gcos 17 - m2gsin 17 - T
The equation was flipped, but I do not understand why. Since blocks are sliding down, shouldn't friction have the negative value because it is going against acceleration??