OPhO Problems and Solutions

An online olympiad open to anyone, first run in May 2020. Teams of up to three enter an Open contest of numerical problems, and the strongest go through to an Invitational round marked from written solutions.

2025

Online

Open
Problems35 problemsProblemsSolutions
  • 1Free Birdnot published
  • 2Racing Linenot published
  • 3The Cake is a Lienot published
  • 4Fiber Opticsnot published
  • 5Cosmological GPSnot published
  • 6Water Dropletnot published
  • 7A Balancing Actnot published
  • 8Bottle trick 1not published
  • 9Bottle trick 2not published
  • 10Frostynot published
  • 11Electric Disconot published
  • 12Bungee Jumpingnot published
  • 13Bouncing Down the Slopenot published
  • 14Gravity Cable Carnot published
  • 15Magnetic Monopolenot published
  • 16Variant Roulette, House Edgenot published
  • 17Squid Gamenot published
  • 18Radioactivenot published
  • 19Arctic Circlenot published
  • 20Hexagons are the Bestagonsnot published
  • 21Spring-loaded capacitornot published
  • 22Supernucleusnot published
  • 23I-Conicnot published
  • 24Problem 24not published
  • 25Relativistic Racenot published
  • 26Glass Blocknot published
  • 27Sproingnot published
  • 28Five Big Boomsnot published
  • 29Hang in there!not published
  • 30Fly Awaynot published
  • 31Unconventional Oscillationsnot published
  • 32Star Powernot published
  • 33Party Poopernot published
  • 34A Cloudy Daynot published
  • 35Airplane, qednot published
Invitational
Part I3 problemsProblemsSolutions
  • 36Theory 1: Magnetosphere & World Eaternot published
  • 37Theory 2: Efficient Lighting & Gas Gas Gasnot published
  • 38Theory 3: On Icenot published
Part II2 problemsProblems
  • 39Theory 4: Paradoxesnot published
  • 40Experimental: Ball Knowledgenot published

2024

Online

Open
Problems35 problemsProblemsSolutions
  • 1Jaywalkingnot published
  • 2Ambidexteritynot published
  • 3Ball Dropnot published
  • 4Coilfunnot published
  • 5Into Orbitnot published
  • 6Roundabout 1not published
  • 7Roundabout 2not published
  • 8Atom Smashernot published
  • 9Dying Lightnot published
  • 10Motorized Pendulum 1not published
  • 11Motorized Pendulum 2not published
  • 12Motorized Pendulum 3not published
  • 13Gravitational Oscillations 1not published
  • 14Gravitational Oscillations 2not published
  • 15Gravitational Oscillations 3not published
  • 16Liquid Lensesnot published
  • 17Electric Slidenot published
  • 18Ping-pong 1not published
  • 19Ping-pong 2not published
  • 20An Envelope of Lightnot published
  • 21Under The Lamplightnot published
  • 22Cannonballnot published
  • 23Filament 1not published
  • 24Filament 2not published
  • 25A Question of Countingnot published
  • 26Peculiar Pumpnot published
  • 27Air Cushionnot published
  • 28Soapy oscillatornot published
  • 29Relativistic Scatteringnot published
  • 30Reluctant Rollernot published
  • 31Solenoid Springnot published
  • 32Devil’s Trillnot published
  • 33Chessnot published
  • 34Conducting sheetsnot published
  • 35A Tired Flappy Birdnot published
Invitational
Theory4 problemsProblemsSolutions
  • 36Penned Particlesnot published
  • 37Bouncy Bubblenot published
  • 38Stellar Shapingnot published
  • 39Hot Solidsnot published
Experimental1 problemIsing Model of FerromagnetismProblemSolution

2023

Online

Open
Problems35 problemsProblemsSolutions
  • 1Coin Flip 1not published
  • 2Coin Flip 2not published
  • 3Highwaynot published
  • 4Spinning Aroundnot published
  • 5Born To Trynot published
  • 6Lightbulbnot published
  • 7Hyperdrivenot published
  • 8Asteroidnot published
  • 9Spaceshipnot published
  • 10Drag 1not published
  • 11Drag 2not published
  • 12Hysteresis 1not published
  • 13Hysteresis 2not published
  • 14Marblesnot published
  • 15Fringe effect approximationnot published
  • 16Sliding Alongnot published
  • 17Space Elevator 1not published
  • 18Space Elevator 2not published
  • 19Laser Powernot published
  • 20Twinkle Twinklenot published
  • 21My Heart Will Go Onnot published
  • 22Tricyclenot published
  • 23Sonic Fryernot published
  • 24Isotope Separator 1not published
  • 25Isotope Separator 2not published
  • 26Somos El Barconot published
  • 27The Final Countdownnot published
  • 28Magnetic Cartsnot published
  • 29De-Terraformingnot published
  • 30All Around The Worldnot published
  • 31Electrostatic Pendulum 1not published
  • 32Electrostatic Pendulum 2not published
  • 33Man In The Mirror 1not published
  • 34Man In The Mirror 2not published
  • 35Funiculì, Funiculànot published
Invitational
Theory3 problemsProblemsSolutions
  • 36Boosternot published
  • 37The Complex Potentialnot published
  • 38General Relativitynot published
Experimental1 problemThe Lorenz SystemProblem
  • 39ExperimentalThe Lorenz SystemProblem

2022

Online

Open
Problems35 problemsProblemsSolutions
  • 1Two Projectilesnot published
  • 2Bow and Arrownot published
  • 3City Lightsnot published
  • 4Springing Earthnot published
  • 5Battle Ropesnot published
  • 6Polarizersnot published
  • 7Fatal Framenot published
  • 8The Wirenot published
  • 9Melting Icebergnot published
  • 10Scalenot published
  • 11Levitatingnot published
  • 12Singing in the Rainnot published
  • 13Rocket Launchnot published
  • 14LC-Diode 1not published
  • 15LC-Diode 2not published
  • 16Raging Loopnot published
  • 17Moon Landingnot published
  • 18Tesseract Oscillationsnot published
  • 19The Roomnot published
  • 20Two Ringsnot published
  • 21Pendulum Circuitnot published
  • 22Broken Tablenot published
  • 23Resistance boxnot published
  • 24Dipole Conductornot published
  • 25Dying Lightnot published
  • 26Tungstennot published
  • 27Bioshock Infinitenot published
  • 28Magnetic Ballnot published
  • 29Magical Balloon 1not published
  • 30Magical Balloon 2not published
  • 31Hydrogen Magnetismnot published
  • 32Relativistic Collisionnot published
  • 33Microscopenot published
  • 34Resistor gridnot published
  • 35Strange Gasnot published
Invitational
Theory5 problemsProblemsSolutions
  • 36Maxwell's Demonnot published
  • 37Euler's Disknot published
  • 38Rocketnot published
  • 39Magical Boxnot published
  • 40Quantum Computingnot published
Experimental1 problemFluid DynamicsProblem
  • 41ExperimentalFluid DynamicsProblem

2021

Online

Open
Problems35 problemsProblemsSolutions
  • 1Fastest Pathnot published
  • 2Resistor Puzzlenot published
  • 3Derby Racenot published
  • 4Cranenot published
  • 5Coaxial Cablenot published
  • 6Magnetic Blocknot published
  • 7Thermal Trainnot published
  • 8Fountainnot published
  • 9Escaping Nieonsnot published
  • 10Pico-Pico 1not published
  • 11Pico-Pico 2not published
  • 12Golden Applenot published
  • 13Free Thrownot published
  • 14Layupnot published
  • 15Right Triangle Potentialsnot published
  • 16Toilet Paper Rollnot published
  • 17Maximum Voltagenot published
  • 18Suspended Rod - 1not published
  • 19Suspended Rod - 2not published
  • 20One Laddernot published
  • 21Two Laddersnot published
  • 22Colliding Conducting Slabnot published
  • 23Evil Gamma Photonnot published
  • 24Spinning Cylindernot published
  • 25Optimal Launchnot published
  • 26Drag on the Platenot published
  • 27Superconducting Loopnot published
  • 28Cantor Interferencenot published
  • 29Solid Core - 1not published
  • 30Solid Core - 2not published
  • 31Solenoidsnot published
  • 32Accelerating Rockets - 1not published
  • 33Accelerating Rockets - 2not published
  • 34Ping Pong - 1not published
  • 35Ping Pong - 2not published
Invitational
Theory4 problemsProblemsSolutions
  • 36Levitationnot published
  • 37Thomas Precessionnot published
  • 38Moving Medianot published
  • 39Missing Energynot published
Experimental1 problemSlit interference via simulation*Problem
  • 40ExperimentalSlit interference via simulation*Problem

2020

Online

Open
Problems55 problemsProblemsSolutions
  • 1Angry Birdsnot published
  • 2The Wheels on the Monster Truck go Round and Roundnot published
  • 3Don’t make me reach my Tipping Pointnot published
  • 4District 12not published
  • 5Neutrino Partynot published
  • 6Quarantine Secretsnot published
  • 7Planetary Protonnot published
  • 8Angel Coasternot published
  • 9Wannabe Twosetnot published
  • 10Waterhorse or Flyinghorsenot published
  • 11Charlie And The Chocolate Factorynot published
  • 12Loopy Wirenot published
  • 13Journey 2: The Magnetic Island 1not published
  • 14Journey 2: The Magnetic Island 2not published
  • 15Tuning Outsidenot published
  • 16Too Much Potentialnot published
  • 17Particle in the Boxnot published
  • 18Room of Mirrors 1not published
  • 19Room of Mirrors 2not published
  • 20Secret Societynot published
  • 21Focus On That Not This! 1not published
  • 22Focus On That Not This! 2not published
  • 23Focus On That Not This! 3not published
  • 24Two Star Crossed Lovers...not published
  • 25Too Borednot published
  • 26You are my Sunshine 1not published
  • 27You are my Sunshine 2not published
  • 28Be Reflected It Mustnot published
  • 29Braking Upnot published
  • 30With Great Powernot published
  • 31I’m a little teacupnot published
  • 32Tetrahedron Resistancenot published
  • 33Aimenot published
  • 34Global Warmingnot published
  • 35Power Dissipationnot published
  • 36Flattening the Curvenot published
  • 37Hiking in Mountainsnot published
  • 38Me and my Crushnot published
  • 39Can’t or cannot published
  • 40Mom Trust the Physics!not published
  • 41Fbi Open Up!not published
  • 42Pappu’s Half Disknot published
  • 43Don’t Fallnot published
  • 44Heartbreaknot published
  • 45Hot or Notnot published
  • 46Sandwiched!not published
  • 47Tom and Jerry 1not published
  • 48Tom and Jerry 2not published
  • 49Tom and Jerry 3not published
  • 50Ghoster Coasternot published
  • 51Galactic Gamesnot published
  • 52Cramped Upnot published
  • 53I knew I should’ve stayed home todaynot published
  • 54Fun with a Stringnot published
  • 55When Rocket Scientists Play Catchnot published
Invitational
Problems10 problemsProblems