Coefficient of kinetic friction, need today

[an9890]

coefficient of kinetic friction, URGENT need today

The system shown in the figure below has an acceleration of magnitude 0.51 m/s2, where m1 =
4.30 kg and m2 = 6.00 kg. Assume that the coefficient of kinetic
friction between block and incline is the same for both inclines.

Link to figure:
http://img9.imageshack.us/img9/3437/figureyh.jpg
m1 is box on the left, m2 is box on the right. both angles are 35 degrees. a) find the coefficient of kinetic friction

Here's what I tried:
coefficient of kinetic friction = (gsinΘ - a) / gcos Θ
and got .63668

when i input my answer in the system said "your answer differs from the correct answer by orders of magnitude."

b) find the tension in the string
T= m1a + m1gsinΘ
= 26.36 N

system said "your answer differs by 10% of correct answer..."Please help. I need this by tonight. Thank you!

 

[hotvette]

Let's start with the basics. What equation of motion (i.e. $$\Sigma$$F = ma) did you use for each mass?

 

[an9890]

^

(a)
∑ Fx = ma --> mgsinΘ - f_k = ma
∑ Fy = 0 --> n - mgcosΘ = 0
n = mgcosΘ
and f_k = mu_kn

so mu_k = (gsinΘ -a) / gcos Θ

 

[hotvette]

∑ Fx = ma --> mgsinΘ - fk = ma

I presume that's for m2. But, you forgot the force of the tension. Also, you need a similar equation for m1. You'll then have two equations in two unknowns (T and mu) that can be solved by substitution.

 

[rdl]

As a scientist, it is important to always double check your equations and calculations to ensure accuracy. In this case, it seems like there may be a mistake in your calculation for the coefficient of kinetic friction. The correct equation for this situation is μk = (m2g - m1a) / (m1gcosΘ + m2gsinΘ). When plugging in the given values, the coefficient of kinetic friction should be 0.313.

For the tension in the string, your calculation is correct. However, it is always important to pay attention to significant figures and round your answer accordingly. In this case, the tension should be rounded to 26.4 N.

As for the urgency of this problem, it is important to prioritize accuracy over speed. Rushing through calculations can lead to mistakes and incorrect results. It is always best to take your time and ensure that your answers are correct. I recommend reviewing the equations and double checking your calculations before submitting your final answer.