I know this is math, but I don't know any physics forum, and I've been a member here a long time and like these people. Anyway, I think it is mostly a math problem.

The lower block in the figure is pulled on by a rope with a tension force of 20 N. The coefficient of kinetic friction between the lower block and the surface is 0.30. The coefficient of kinetic friction between the lower block and the upper block is also 0.30.

What is the acceleration of the 2.0 kg block?

http://jjoshua2.googlepages.com/a.p8.28.jpg
Thats what it looks like.

The answer is 1.77 m/s^2 the book says and that is what I got. Now on the test there is an almost identical problem, same picture.

http://jjoshua2.googlepages.com/knight_Figure_08_28.jpg
A rope pulls on the lower block in the figure with a tension force of 20 N. The coefficient of kinetic friction between the lower block and the surface is 0.37. The coefficient of kinetic friction between the lower block and the upper block is also 0.37. What is the acceleration of the 2.0 kg block?

It says the answer is 2.7, which I guessed since it was the lowest answer, but I think the answer should be lower than 1.77, I calculated about 0.6.

I can ask my teacher in a couple days, but she'll probably get mad at me if I bother her with what should be a non-issue.

Thanks so much!