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A 5.00 kg block is pulled along a horizontal frictionless floor by a cord that exerts a force of magnitude 12.0 N at an angle of 25 degrees above horizontal. a) make a free-body diagram and determine the magnitude of the block's velocity b) the F magnitude is slowly increased. What is the value (of the force, I'm assuming) just before the block is lifted (completely) off the floor? c) What is the magnitude of the block's acceleration just before it is lifted (completely) off the floor.

OK, I have done part a), drawing the free body diagram and figured out the magnitude of the acceleration (+2.17m/s^2). I also know that to do b), I need to find the value of the force when the normal force is equal to zero. From there, I can't figure out where to go.

If someone could help me out with an equation to use and/or other tips, it would be much appreciated.

Chris