v = d/t Formula – How to Calculate Velocity (Practice)
v = d/t — Average speed (or velocity along a straight path)
Average speed is distance divided by time: v = d/t. Along a straight line with a direction, the same ratio is average velocity. Always convert units before dividing.
Guide — how to use this formula
- 1. Convert distance to metres and time to seconds when the answer unit is m/s.
- 2. Compute v = d/t, or rearrange for d or t.
- 3. For multi-leg trips, add distances and times first.
- 4. m/s → km/h: multiply by 3.6.
Derivation
Average velocity is defined as displacement (or distance for speed) per unit time:
- Definition for a trip of length d lasting time t:
v = \frac{d}{t} - Rearrangements:
d = vt,\quad t = \frac{d}{v}
Don’t average two leg speeds for overall average — use total distance ÷ total time.
Examples
Example: 120 m in 10 s
v = 120/10 = 12 m/s.
Example: minutes trap
600 m in 2 min → t = 120 s → v = 5 m/s (not 300).