Kinematics Equations: Which One Do I Use?
Pick the right kinematics equation by listing what you know, then solve two worked examples for velocity and distance.
The three equations
- v = v₀ + at
- Δx = v₀t + ½at²
- v² = v₀² + 2aΔx
They work only when acceleration is constant.
Pick one fast
- List what you know and what you want
- Choose the equation that has no unknown extras
- Keep units in meters and seconds
Write v₀, v, a, t and Δx before you choose.
Example 1
A car starts from rest and accelerates at 2 m/s² for 5 s. Find v.
- v₀ = 0, a = 2, t = 5
- v = 0 + (2)(5)
v = 10 m/s
Example 2
Same car. How far does it travel in those 5 s?
- Δx = v₀t + ½at²
- Δx = 0 + ½(2)(5²)
Δx = 25 m
Common mistake
Use these equations when acceleration keeps changing
They assume constant acceleration.
Check that a stays the same before you use them.
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