tion:How can I know when I should use the 3 equations of motion in problems?Ad by Cue Learn Private LimitedLearn math as logic. Not rules.Get ahead at math, get ahead at everything else. Live online CLASSES for kids in grades K-10.Learn More15 Questions and AnswersPatrick Hochstenbach, Master Theoretical Physics, Radboud University, the NetherlandsUpdated 6 years ago · Author has 2.7K answers and 2.5M answer viewsHow can I know when I should use the 3 equations of motion in problems?Originally Answered: How can I know that when I should use the 3 equations of motion in problems?The three equations of motions are:1) v = v0 + aΔt2) x = x0 + v0Δt + ½aΔt^23) v^2 = v0^2 + 2a(x − x0)These are the equations you learn in the physics class at school to calculate the velocity or end position of an object GIVEN an acceleration and a time or a distance.Let me tell you a little secret: there are no 3 equations of motion. The three THINGS you see above follow DIRECTLY from the definition of a constant acceleration in one direction. But you need a bit of calculus to see that. The 3 above are an easy way to calculate things without needing calculus.To know which one you need requires a close examination of your physics problem. E.g.Equation 1) you use when the physics teacher asks you to calculate a speed, given some actions during a period of time.Equation 2) you use when the physics teacher asks you to calculate a position, given some actions during a period of time.Equation 3) you use when the physics teachers asks you to calculate a speed, given some actions over some distance.Lets try this out!Equation 1: gives you a speed as answer and it needs a time as input.What is the speed of Jan when she travels at 10 m/s without accelerating for 10 seconds?Answer:v0 = 10 m/s ; a = 0 m/s^2 (she isn't accelerating) ; Δt = 10 sSo, v = 10 + 0 * 10 = 10 m/sWhat is the speed of Jan when she travels at 10/ms and decelerates at 10 m/s^2 for 2 seconds?Answer:v0 = 10 m/s ; a = -10 m/s^2 ; Δt = 2 sSo, v = 10 + -10 * 2 = - 10 m/s (she travels in the opposite direction)Equation 2: gives you a position as answer and needs a time as input.Jan travels at 10 m/s without acceleration where is she 10 seconds later?Answer:x0 = A (some point in space) ; v0 = 10 m/s ; a = 0 ; Δt = 10 sSo, x = A + 10 * 10 + ½ * 0 * 2^ 2 = A + 100 meter.I don't know where A is but Jan is 100 meters further on her route.Jan travels at 10 m/s , decelerates at 10 m/s^s for 2 seconds, where is she now?Answer:x0 = A (some point in space) ; v0 = 10 m/s ; a = -10 m/s^2 ; Δt = 2 sSo, x = A + 10 * 2 + ½ * - 10 * 2 ^ 2 = A + 20 - 20 = AI don't know where A is but that is where Jan is now.