drvheadline[0] = ["Step","Reason","1. vf = vi + at",
"first motion equation",
"2. vf = vi + (1.21 m/s2)(3.14 s)",
"substitute values",
"3. vf = vi + 3.80 m/s",
"multiply",
"4. Δx = ½(vi + vf)t",
"second motion equation",
"5. 11.8 m = ½(vi + vf)(3.14 s)",
"substitute known values",
"6. 7.52 m/s = vi + vf",
"multiply by 2, divide by 3.14 s",
"7. 7.52 m/s = vi + vi + 3.80 m/s",
"substitute equation 3 into equation 6",
"8. vi = 1.86 m/s",
"solve for vi",
"9. vf = vi + 3.80 m/s = 5.66 m/s",
"from equation 3"];
drvNarration[0]=["We start with a motion equation that contains the two values we want to find.
",
"We substitute the known values into the equation.
",
"We multiply the known values.
",
"Now we write another motion equation with the velocities we want to find.
",
"We substitute the known values for displacement and elapsed time.
",
"We simplify the equation by multiplying and dividing out the factors on the right side. This gives us a second equation with the two velocities.
",
"We substitute the expression for vf from equation 3 into equation 6…
",
"…and solve for vi.
",
"Then we use equation 3 to find vf."];
drvStepBreak[0]=[3,3];
drvExplanation[0]=["We start with a motion equation containing the two velocities we want to find, and substitute known values, and simplify.",
"Now we use a second motion equation containing the two velocities, substitute known values, and simplify. This gives us two equations with the two unknowns we want to find.",
"Now we solve the two equations."]