What is the correct force to accelerate a block on an incline?

[nokia8650]

I am struggling with the following problem:

http://img50.imageshack.us/img50/2682/img184yj5.th.jpg http://g.imageshack.us/thpix.php

http://img407.imageshack.us/img407/9342/img182et8.th.jpg

I have found that the resultant force on the block must be 500N, and therefore the force supplied must be 1500N. However, I then get a ratio of 30 for the area - the correct answer is 10 in the back of the book.

Thanks for any help in advance

 

[Redbelly98]

Hmmm ... your answer makes sense to me. It's as if they forgot to include the block's weight in the calculation.

(This would be an unwieldy method for accelerating the block anyway, since the device would have to be at least 250m high.)