Meeting and Catch-Up Calculator
Find when two travelers meet or one catches the other at constant speed. Choose directions, mix speed units and compare signed positions over time.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Place A at position 0 and B at the initial positive separation. Assign signed velocities from the direction scenario. Equate xA=vAt and xB=D+vBt. A future meeting requires positive closing speed unless both start together.
t=D/(vA−vB), when D>0 and vA>vB; xA=vAt; xB=D+vBt
Worked example
Travelers 6 km apart moving toward each other at 12 and 6 km/h meet after 1/3 hour, or 20 minutes, at 4 km from A’s start. In the same direction, A catches B after 1 hour at position 12 km. Moving apart, they do not meet in the future.
Assumptions and input details
Both travelers start at the same time and maintain constant speeds on a straight line. Speeds are nonnegative magnitudes; the direction selector sets signs. B initially lies to the right of A. Zero separation gives a meeting at time zero; equal velocities then remain coincident. A slower or equally fast traveler cannot catch a traveler already ahead. The graph uses the entered duration and may end before a calculated meeting; no stopping after a meeting is assumed. Input base quantities are capped at 1e12 meters, m/s or seconds; graph duration is positive.
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
Choose from 23 length definitions, including explicitly labelled regional measures. Area conversions square the length factor; geometric volumes cube it.
Regional measures are not interchangeable merely because their names look similar. This is a documented selection, not a claim to include every historical unit.
NIST measurement tables · Japanese traditional units · Mainland China and Hong Kong unit distinctions
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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