- #1

cleverfield

- 12

- 0

## 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!