Some students placed a clear solution in a beaker and heated it for 40 minutes. Their observations are provided. Time (minutes) Observations 10 Bubbles on the bottom of the beaker are visible 20 Water is rapidly boiling 30 Water level in beaker has decreased 40 White crystals have formed on the edges of the beaker Evidence that the solution contained matter that could not be seen was observed during what time? 10 minutes о O 20 minutes O 30 minutes O 40 minutes​

Aparticle's position is given by x = 3.00 - 9.00t + 3t2, in which x is in meters and t is in seconds. (a) what is its velocity at t = 1 s? (b) is it moving in the positive or negative direction of x just then? (c) what is its speed just then? (d) is the speed increasing or decreasing just then? (try answering the next two questions without further calculation.) (e) is there ever an instant when the velocity is zero? if so, give the time t; if not, answer "0". (f) is there a time after t = 3 s when the particle is moving in the negative direction of x? if so, give the time t; if not, answer "0".