Euler's formula, level of reflection at surface for bouncing ball python

Question

This code below models perfect reflection of a bouncing ball. What would model 90%?

for i in range (steps):
   t[i+1] = t[i] + dt
   x[i+1] = x[i] + v[i]*dt
   v[i+1] = v[i] - g*dt
   if x[i+1] < 0.0:    # if ball is below surface, reflect it
      x[i+1] = -x[i+1]
      v[i+1] = -v[i+1]

Answer 1

This

  v[i+1] = -v[i+1]

is equivalent to

  v[i+1] *= -1

So try

  v[i+1] *= -0.9