# Finding acceleration and tension on an incline

1. Oct 5, 2013

### soysauce

1. The problem statement, all variables and given/known data
Hi everyone, I hope you're enjoying your weekends!
I've been trying this question for a while not having any luck, I'm hoping someone can tell me where I'm going wrong

The question is:
Two boxes are connected by a rope that passes through a pulley on the corner of a incline. Box A is 2.5 kg and box B is 5.5 kg. The coefficient of kinetic friction on the incline is 0.54. Box A is on the incline and box B hangs over. The angle of the incline is 25.4º. Find the acceleration and the tension.

The answers given are 3.8 m/s2 [down] and 33 N [up]

2. Relevant equations

I got these equations from here:https://www.physicsforums.com/showthread.php?t=27346 and I understand why I would use them

Ft = m1 *a + m1gcosθ + μm1gcosθ and
Ft = m2(g-a)

3. The attempt at a solution

m1 = 2.5 kg, m2 = 5.5 kg, μ = 0.54, θ = 25.4°

I know I can equate the two tension equations to get:

m2(g-a) = m1 *a + m1gcosθ + μm1gcosθ

But when I plug in the known values and solve:

5.5(9.8-a) = 2.5*a + 2.5*9.8*cos(25.4) + 0.54*2.5*9.8cos(25.4)

I get a value of a = 2.4

Could someone tell me where I'm going wrong here?

2. Oct 5, 2013

### Staff: Mentor

In that first equation, one of those cosines should be a sine.

But please don't use someone else's derived equations. Derive them yourself, using Newton's 2nd law. Then you'll understand where they come from.

3. Oct 5, 2013

### soysauce

Whoops, that's true!
Thanks so much, I'll definitely be sure to in the future.