unfortunatly I failed my first physics exam. I have to go back through and correct the ones I missed. I need some help on the ones im stuck on. any help and explanations is greatly appreciated. 1.) three blocks are being accelerated upward by a force applied to the bottom block. the mass of the bottom block is 3kg, the middle block is 6kg, the top block is 9kg. The blocks are accelerating at 3.2 m/s. what is the net force on the middle block? would it just be mass x acceleration? (6x3.2)? 2.) A person can swim with a speed of 3 m/s in still water, and wants to get to the other side of a 400m wide river whos water flows 2 m/s downstream. if she swims acress in such a way that the time taken is the smallest possible, how far downstream is she swept on the opposite bank? ( i calculated 133.3 seconds and a distance of 267m) I need to find out to how to get her speed relative to the earth?? my choices are 1.6,2.2,3.6,4.3 or 5.0. thought it was distance/time but none of those answers worked. 3.) Two blocks are being pulled along by a constant force of 25N(pulling on B). Block A has a mass of 2kg and black B has a mass of 5kg. (I calculated the tension which is 7.14N) Now it says the blocks encounter a region of friction and the same 25n force is applied but now they are moving with constant velocity. what is the net force on block A? what is the coefficient of friction? 4.)A bucket of water is swung around in a vertical circle with enough speed so the water stays in the bucket. the total mass of water + bucket= 5kg. what is the minimum speed so that water does not leave? If the bucket handle is only capable of applying a force of 172N what is the maximum speed you can swing the bucket?