A reflecting surface reverses the photon momentum instead of absorbing it, so the impulse handed over doubles relative to the absorber case at the stated incidence angle. The arithmetic is exact only for the stated irradiance, area, time, and a perfect reflector at the stated angle. Real beams add finite bandwidth, alignment error, nonideal reflectivity, surface roughness, detector calibration, and measurement/source uncertainty.
Mirror impulse is checked through doubled pressure and force over time. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Mirror impulse comes from doubled pressure
The mirror path is checked through pressure, force, and time.
Jmirror=Ft=6⋅4=24kgm/s
The absorber momentum equality is off
The mirror lesson leaves the absorber momentum closure disabled.