1. The problem statement, all variables and given/known data Determine the speed with which the earth would have to turn to rotate on its axis so that a person on the equator would weigh 3/4 as much 2. Relevant equations VT=r*ω ; Vi=469 m/s is tangential velocity of earth ƩF=M*ac=m*Vt^2/r 3. The attempt at a solution The positive direction is toward the center of the earth. From ƩF=m*ac Initial: m*g-Ni=m*Vi^2/r Final: 3/4m*g-Nf=m*Vf^2/r Since m*g is the same for initial and final state I assume that Ni=Nf Therefore:3/4m*g-[mg-m*Vi^2/r]=m*Vf^2/r or Vf=Sqrt(Vi^2-r*g/4) I have a sign error. I end up taking the square root of a negative number but the physics looks OK. Suggestions?