1. The problem statement, all variables and given/known data
A car is slowing down at a rate of 20 km/h/s. How far does it travel if its original velocity is 50 km/h and its final velocity is 5.0 m/s?

2. Relevant equations

v_f² = v₀² + 2aΔx

3. The attempt at a solution

v_f² = v₀² + 2aΔx
Δx = (v_f² – v₀²) / 2a
= (18²-50²) / 2(-20)
= -2176 / -40
= 54.4 m

That’s wrong, though. The answer should be 15 m.