4 Tricks For Solving Any Physics Problem

Posted by Jacob on 10/26/16 6:14 PM

Screen Shot 2016-10-26 at 6.10.45 PM.pngPhysics can be intimidating, all those pulleys and protons and projectile motion. If you approach it with the right mindset, however, even the hardest problems are usually easier than you think. When you come up against a tough question, don’t panic. Instead, start with these short, easy tricks to help you work through the problem. 

1. What is the subject?

Just about every physics question is testing specific knowledge. When you read the question ask yourself, is it exploring electricity? Torque? Parabolic motion? Each topic is associated with specific equations and approaches, so recognizing the subject will focus your effort in the right direction. Look for keywords and phrases that reveal the topic. 

2. What are you trying to find?

This simple step can save a lot of time. Before starting to solve the problem, think about what the answer will look like. What are the units; is the final answer going to be in kilograms or liters? Also consider what other physical quantities might relate to your answer. If you’re trying to find speed, it might be useful to find acceleration, then solve that for speed. Determining restrictions on the answer early also ensures you answer the specific question; a common mistake in physics is solving for the wrong thing. 

3. What do you know?

Think about what details the problem mentions. Unless the question is really bad, they probably gave you exactly the information you need to solve the problem. Don’t be surprised if sometimes this information is coded in language; a problem that mentions a spring with “the mass removed from the end” is telling you something important about the quantities of force. Write down every quantity you know from the problem, then proceed to…

4. What equations can you use?

What equations include the quantities you know and also the one you’re looking for? If you have the mass of an object and a force and you’re trying to find the acceleration, start with F=ma (Newton’s second law). If you’re trying to find the electric field but you have the charge and the distance, try E=q/(4πε*r2). 

If you’re having trouble figuring out which equation to use, go back to our first trick. What equations are associated with the topic? Can you manipulate the quantities you have to fit in any of them? 

Bonus Trick: “Hack” the units

This trick doesn’t always work but it can jumpstart your brain. First, determine the units of the quantity you’re trying to find and the quantities you have. Only use base units (meters, kilograms, seconds, charge), not compound units (Force is measured in Newtons, which are just kg*m/s2). Multiply and divide the quantities until the units match the units of the answer quantity. For example, if you’re trying to find Potential Energy (kg*m2/s2) and you have the height (m), mass (kg) and gravitational acceleration (m/s2), you can match the units by multiplying the three quantities (m*kg*m/s2=kg*m2/s2).

Note: Unlike the other ones, this trick won’t always work. Watch out for unitless constants. For example, Kinetic energy is ½*mass*velocity2, not just mass*velocity2 as the units suggest. Even though this trick isn’t perfect, however, it can still be a great place to start.

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For more relevant reading, check out these other blog posts written by our physics tutors in New York and Boston:

Inertia Experiments & Rolling Motion Part I

Inertia Experiments and Rolling Motion Part II

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