This is a very old topic that I wanted to "publicize". My contention is that you cannot use power to calculate acceleration without first converting power to force. It is possible to calculate an acceleration by assuming some period of time to calculate a change in energy, but this method does not yield instantaneous acceleration. It seems trivial, but take a look at this spreadsheet. http://spreadsheets.google.com/ccc?key=pBCH2ClzmrplHUNFgrkT7HA I've seen many, many equations that claim to do this calculation, but not one of them worked, and the ones that worked had the conversion from power to force buried in constants. So before posting any formulas please try them out with the spreadsheet to make sure they work.