I don't believe that this problem is difficult, but I am unsure of myself as to the answers. The position of the particle moving along an x axis depends on the time according to: x = ct^2 - bt^3 (x in meters and t in seconds) a) what units must c and b have? Let their numberical values be 3.0 and 2.0, respectively. b) At what time does the particle reach its maximum positive x position? This is what I did: a) m - cs^2 - bs^3 --> ms^2/2^2 - ms^3/s^3 = m - m = __ m so, c = m/s^2 and b = m/s^3 b) x = ct^2 - bt^3 i am imagining the particle to be something like a ball thrown in the air. is this a good idea? with that in mind, i would imagine the velocity of the ball at the max point would be 0, so: v = x' = 6.0t - 6.0t^2 = 0 --> t=1 or t = 0 i am ruling out t = 0, because that is the starting time so i believe that the time it reaches it's max position is at 1.0 seconds. was my process for a and b correct?