How can the required force be calculated for pushing a block up an incline?

[henlet]

Homework Statement

as a new physics student, I'm not sure how to derive the formula i need to answer this question.

there's a ramp that rises 1m in height and 20m in length. a block weighing 20,000kg needs to be pushed up it. (yup, we're building the pyramids). how much force is needed to push the block up the ramp?

Homework Equations

so i know that net force = mass * acceleration.
i also think that the net force downhill along this ramp is 1m/20m or .05% of the block's weight, which is 1000kg.
the book tells me the answer is 9800N.

The Attempt at a Solution

9800 N = 20,000kg * acceleration
where N = kgm/s2
acceleration = .49 m/s2, but why? and i suppose the book is rounding in some way to come up with 9800 N instead of 10,000?

 

[andrien]

9.8*.05.your answer is 1000 kg right.multiply by g to find in N.I hope you know what is g.

 

[azizlwl]

If you have the block fall directly to earth, then you have an acceleration g=9.8m/s<sup>2/SUP]. You need force of mg to lift the block.

Now imagine if the block slide down the ramp. The acceleration must be slower than the direct drop.

Now you have mass and new acceleration value.</sup>