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## Homework Statement

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 .

## Homework Equations

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??