1. The problem statement, all variables and given/known data An object of mass m falls from rest subject to air resistance force directly proportional to the object's speed, F=-bv, where b is the proportionality constant in N/(m/s) and the negative sign indicates the direction of the force opposite to the direction of the velocity. How long does it take this object to reach half of its terminal speed? 2. Relevant equations a=g-bv/m, a=dv/dt, etc... 3. The attempt at a solution tried, all failed.