Solving "An Person Pushes a Box Up a Hill: A Physics Problem

[danago]

Hey. I've been given this problem:

"An person wishes to push a box up a hill, inclined at 30 degrees. He is able to push with a force of 450N. If the box has a mass of 20kg, and a force of friction with magnitude 20N applies, what is the acceleration of the box?"

I drew a diagram, and came up with this:
http://img135.imageshack.us/img135/1124/incplaneob0.gif

What i did was resolve all of the forces into their components (parallel and perpendicular to the slope), including the weight and normal force, and then add them all.

I got an answer of 16.6 $$ms^-2$$, but apparently the answer is 1.9 $$ms^-2$$. Would someone be able to maybe quickly work it out, and tell me what the real answer is?

Thanks very much,
Dan.

 

[Päällikkö]

(450-20-20*9.81*sin(30))/20 = 16.595, so you should be correct. The box should have an acceleration plenty over 1.9 m/s² even if the hill was vertical.

 

[danago]

ok thanks for confirming that :-)