drvheadline[0] = ["Step","Reason","1. ",
"position equation",
"2. ",
"relation between velocity and position",
"3. ",
"calculate the derivative",
"4. ",
"solve for t when velocity is zero",
"5. ",
"identify sign of velocity during each interval",
"6. ",
"relation between acceleration and velocity",
"7. ",
"calculate the derivative",
"8. ",
"solve for t when acceleration is zero"];
drvNarration[0]=["We start with the equation that gives the position of the car in meters. ",
"The velocity is the time derivative of position. ",
"We calculate an expression for the velocity by taking the derivative of the position function. ",
"Set the expression for velocity equal to zero and solve for the time, by factoring as shown. ",
"Pick a time value and find the sign of the velocity, or look at the sign of the slope of the position-time graph during each time interval. ",
"The acceleration is the time derivative of velocity. ",
"We calculate an expression for the acceleration by taking the derivative of the velocity function. ",
"Set the expression for acceleration equal to zero and solve for the time at which the instantaneous acceleration is zero."];
drvStepBreak[0]=[4,1];
drvExplanation[0]=["",
"These are the only times where the velocity can change sign, that is, when the object can change direction.",
"We have now identified the time interval, , during which the velocity is negative. Next we find the time(s) at which the instantaneous acceleration is zero."]