Impulse is area under force-time, not peak force
The mistake
Using the maximum force in a collision as if it were the impulse.
Why it feels right
Peak force is easy to read directly, while impulse requires the area over the entire collision interval.
How to catch it
Your impulse has units of newtons instead of newton-seconds.
The first principle
Impulse is J = ∫F dt = Δp. A longer, smaller force can deliver the same impulse as a shorter, larger force.
worked mini-example
A triangular force-time pulse has height 100 N and width 0.20 s. Impulse?
Common wrong move
100 N.
Correct
Area = ½(0.20)(100) = 10 N·s.
Test the repair MOM-08 · transfer
include N·s
Make a fresh prediction before referring to the worked example.