Physics Variable Extractor Text
Solve for any variable in common physics equations such as v = u + at, F = ma, KE = 1/2 mv^2, V = IR and PE = mgh with step-by-step rearrangement in SI.
Formula
Multiple: v=u+at, F=ma, KE=0.5mv^2, W=Fd cos(theta), V=IR, P=W/t, PE=mgh
Select a physics formula and choose which variable to solve for. The calculator algebraically rearranges the equation, substitutes known values, and computes the answer with step-by-step work shown. All standard SI units are used.
Worked Examples
Example 1: Finding Final Velocity (Kinematics)
Problem:A car starts from rest (u=0 m/s) and accelerates at 3 m/s^2 for 8 seconds. Find final velocity.
Solution:Using v = u + at v = 0 + (3)(8) v = 0 + 24 v = 24 m/s
Result:Final velocity: 24.0000 m/s (about 86.4 km/h)
Example 2: Finding Resistance (Ohm Law)
Problem:A circuit has 12V across it and draws 0.5A of current. Find the resistance.
Solution:Using R = V/I R = 12 / 0.5 R = 24 ohms
Result:Resistance: 24.0000 ohms
Frequently Asked Questions
How does the physics variable extractor work?
Physics Variable Extractor Text takes a physics formula and algebraically rearranges it to solve for any unknown variable. You select the equation, choose which variable to solve for, and enter the known values. The calculator then applies the rearranged formula and shows step-by-step work. For example, if you know force (F) and mass (m) from Newton second law F=ma, it rearranges to a=F/m and computes acceleration. This process of extracting a variable from an equation is fundamental to physics problem-solving and is one of the first skills taught in introductory physics courses.
What is the difference between kinematics and displacement equations?
Both are kinematic equations but describe different relationships. The equation v = u + at relates final velocity to initial velocity, acceleration, and time, without involving distance. The equation s = ut + 0.5at^2 relates displacement to initial velocity, acceleration, and time, without involving final velocity. These are two of the four SUVAT equations used in constant-acceleration problems. The choice of equation depends on which variables are known and which is unknown. If the problem does not mention displacement, use v = u + at. If it does not mention final velocity, use s = ut + 0.5at^2.
Why does the work formula include cos(theta)?
Work is defined as the dot product of force and displacement vectors: W = F * d * cos(theta), where theta is the angle between the force direction and the direction of motion. When force is applied in the same direction as motion (theta = 0 degrees), cos(0) = 1 and all the force contributes to work. At 90 degrees (perpendicular), cos(90) = 0 and no work is done, like carrying a box horizontally where gravity acts vertically. At angles between 0 and 90, only the component of force along the direction of motion does work. Negative work (theta > 90) means force opposes motion, like friction.
When does the displacement equation produce two solutions?
The displacement equation s = ut + 0.5at^2 is quadratic in time (t), so solving for t can produce two solutions. Physically, this occurs when a projectile reaches a certain height twice: once going up and once coming down. The calculator returns the positive root, which is typically the physically meaningful answer. A negative discriminant (no real solutions) occurs when the displacement is unreachable given the initial velocity and acceleration, for example trying to reach 100m height when thrown with insufficient velocity. Understanding when equations have multiple solutions is important for correctly interpreting physics problems.
How is Ohm Law related to power and energy equations?
Ohm Law (V = IR) connects voltage, current, and resistance in a circuit. Combined with the power equation (P = W/t), it yields useful relationships: electrical power P = VI = I^2R = V^2/R. These allow you to calculate any electrical quantity if two others are known. For example, a 60W light bulb on a 120V circuit draws I = P/V = 0.5A of current and has R = V/I = 240 ohms resistance. The energy consumed equals power multiplied by time: E = Pt. Understanding these interconnected formulas is essential for circuit analysis, electrical engineering, and even understanding your electricity bill.
What are the four SUVAT equations, and which ones are not offered here?
The constant-acceleration set links the five quantities s, u, v, a and t, and each equation omits exactly one of them. This tool provides v = u + at, which omits displacement, and s = ut + 0.5at squared, which omits final velocity. The other two are v squared = u squared + 2as, which omits time, and s = ((u + v) / 2) x t, which omits acceleration. The last pair is worth knowing because when time is not given, v squared = u squared + 2as answers directly instead of forcing you to solve a quadratic for t first and substitute.
How does dimensional analysis confirm a rearranged formula is correct?
Rewrite both sides in base units and check they match. Newton's second law rearranged to a = F / m gives newtons per kilogram, and a newton is kg m per second squared, so the kilograms cancel and you are left with metres per second squared, which is acceleration. Kinetic energy is another example: kg multiplied by (m/s) squared gives kg m squared per second squared, which is the joule. If a rearrangement leaves you with the wrong dimensions, the algebra went wrong somewhere, and the check costs seconds. It cannot catch a missing dimensionless factor such as the one half.
What is the difference between kinetic energy and momentum?
Momentum is mass times velocity and is a vector, so direction matters and it is conserved in every collision. Kinetic energy is one half mass times velocity squared, is a scalar, and is conserved only in elastic collisions. The squared term is the practical difference: doubling speed doubles momentum but quadruples kinetic energy, which is why stopping distance grows with the square of speed while the impulse needed scales linearly. When solving for velocity from kinetic energy Physics Variable Extractor Text takes a square root, so it returns the positive magnitude and loses the direction that momentum would preserve.
Why is g fixed at 9.81 m/s squared, and when does that matter?
The gravitational potential energy relation uses a constant surface value rather than an input. Standard gravity is defined as 9.80665 m/s squared, and the true local value ranges from about 9.78 at the equator to about 9.83 near the poles because of Earth's rotation and oblateness, a spread of roughly half a percent. That is negligible for coursework and well below the precision of most measured masses and heights. It does matter for precision gravimetry, and mgh itself breaks down once the height is large enough that gravity weakens appreciably with distance from the centre.
What does a negative answer mean in these equations?
It means the quantity points opposite to the direction you implicitly chose as positive when entering the values. A negative acceleration in v = u + at is deceleration only if the velocity is positive; with a negative velocity the same sign means speeding up in the other direction. Negative work from W = Fd cos(theta) arises when the angle exceeds 90 degrees, meaning the force opposes the motion, as friction does. Fix one positive axis before entering anything and keep every input consistent with it, since the algebra has no way to warn you about a mixed convention.
References
Background & Theory
History
Reviewed for accuracy by Daniel Agrici, Founder & Lead Developer ยท Editorial policy
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