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# Two Common Math Mistakes on MCAT Physics

July 23, 2017

Physics plays a relatively minor role in the new MCAT. In fact, only one quarter of the questions on the Chemistry/Physics section actually test general physics knowledge. From my experience teaching MCAT physics, many mistakes people make on this section of the exam are due to errors in mathematical reasoning rather than physics content knowledge. Two common mistakes include:

1. Units

When carrying out calculations on the MCAT, be mindful of the units attached to each variable. Topics like hydrostatic pressure and buoyancy, for example, often require equations involving density. In general chemistry class, we learned that the density of water is 1 g/mL. However, on the MCAT density of water is more often written as 1000 kg/m3. Although both values are correct, each has an appropriate context, and knowing when to use each value for the density of water makes the difference between a point won and lost.

Furthermore, test-takers should be aware of the meaning of each unit. For instance, did you know that 1 volt is equivalent to 1 Joule / coulomb? Or the fact that 1 Pascal is equivalent to 1 N / m2? Many of the physics questions on the MCAT require students to manipulate equations and subsequently derive units for a novel variable. To do so, it is essential to understand the SI units that make up amperes (coulombs per second), torque (Newton meters), etc.

1. Angles

Several physics equations on the MCAT include angles – Snells’s law, work, and magnetic force to name a few. Understanding how to measure these angles is essential to properly using the equations involved. For instance, the angles described in Snell’s law (n1sin θ1 = n2sinθ2)are measured with reference to the normal and not to the surface between two adjacent media. When calculating work using the equation W = Fd cosθ, theta is the angle between the force vector and the distance vector. In other words, when the force pushing in the same direction as the distance vector, work is equal to force times distance (since cos(0o) = 1).

In addition, be sure to memorize the values of common trigonometric functions, such as the sine, cosine, and tangent of 0o, 30o, 45o, 60o, and 90o. The writers of the MCAT are well aware that calculators are not allowed on the test, so you will not be expected to know any non-standard geometric values (e.g. sin(74o)).

It doesn’t matter whether you were a math major in college or never took any math course beyond Algebra II since the calculation questions on the MCAT are all based on simple algebraic, geometric, and trigonometric functions. Still, practicing is critical to being able to use them effectively on the MCAT. A motto I often repeat to students, “Perfect practice makes perfect,” means that avoiding these common mistakes on the MCAT begins with practicing proper math and physics techniques while studying at home. In short, treat each practice question as if it were part of the actual MCAT.