.041=.5*.0042*v^2

Solution for .041=.5*.0042*v^2 equation:

Simplifying
0.041 = 0.5 * 0.0042v2

Multiply 0.5 * 0.0042
0.041 = 0.0021v2

Solving
0.041 = 0.0021v2

Solving for variable 'v'.

Move all terms containing v to the left, all other terms to the right.

Add '-0.0021v2' to each side of the equation.
0.041 + -0.0021v2 = 0.0021v2 + -0.0021v2

Combine like terms: 0.0021v2 + -0.0021v2 = 0.0000
0.041 + -0.0021v2 = 0.0000

Add '-0.041' to each side of the equation.
0.041 + -0.041 + -0.0021v2 = 0.0000 + -0.041

Combine like terms: 0.041 + -0.041 = 0.000
0.000 + -0.0021v2 = 0.0000 + -0.041
-0.0021v2 = 0.0000 + -0.041

Combine like terms: 0.0000 + -0.041 = -0.041
-0.0021v2 = -0.041

Divide each side by '-0.0021'.
v2 = 19.52380952

Simplifying
v2 = 19.52380952

Take the square root of each side:
v = {-4.418575508, 4.418575508}