Many students need help getting started on physics homework problems. Here is a general strategy that can apply to many types of problems.
For many students, the hardest part of a beginning physics class is problem solving. If you are to succeed in physics, you must learn to solve problems. This article outlines a basic problem solving strategy. It is designed for physics problems but can also apply to problems in areas other than physics, especially for homework in other science, physical science, and math classes. Try it. Textbooks also often give specific strategies for particular classes of problems.
- Hide your calculator: Most beginning students start by taking out their calculators and punching numbers. No!!!!!!! Save this for the last step, after you know what numbers to punch.
- Description: Read the problem carefully, looking for key words. Make sure you understand what is being asked. Differentiate between the relevant and irrelevant information. Translate the problem into your own words. List all the information given in the problem, explicit and implied, and of the desired information.
- Visualize: Draw a picture of the situation. If the problem is a motion problem draw a motion diagram showing the positions, velocities, and accelerations. If the problem is a force problem, draw a free body diagram of the forces involved. For a collision problem draw the objects before and after the collision, and so on. Do this step carefully and include all relevant information. Make sure to take care of details like explicitly defining your coordinate axes, positive directions, and zero points so you can remember these details and use them consistently throughout the problem.
- Qualitative solution (no numbers): Translate the problem from English words to equivalent physical principles. What basic principles are involved? For many people this translation is the most difficult part of solving a problem. Work on it. Also, make a guess as to the final solution, or basic form of the solution. This guess should be based on previous experience or physical intuition. Why do you think this is the basic form of the solution?
- Planning: Select the equations that apply to the problem, keeping in mind the physical principles involved from the last step. Outline how to use the basic equations to get from the given information to the desired information. Except in the simplest problems, getting from the given to the desired information will require several steps, but if you outline the procedure properly, the problem is essentially solved. If all else fails and you are clueless about how to proceed, write down all the equations that apply to the problem. Make sure the equations apply and fill in the known quantities to see what you can learn. This is not the ideal approach, but it has been known to work when the problem solver is otherwise at a total loss.
- Solution: Carry out the plan. Solve the problem algebraically first, as far as possible, to obtain an algebraic solution to the problem. Finally as a last step, plug in the numbers and perform the numerical calculations. Now you may pull out your calculator. If you have done the previous steps properly, the actual solution of the problem should be fairly easy.
- Checking: Check to make sure you have done all the preceding steps correctly. Think about the answer. Does it make physical sense? If not, write down why it doesn't (especially on a test) and check all preceding steps again. A fairly quick check to perform is to check the units. If the units don't work out right, you did something wrong. Check all the preceding steps again. Next look for special cases. Often the solution for a special case is already known from personal experience. See if your solution works for these special cases. What happens if you set one of the variables equal to zero, infinity, etc.? Another variable? Checking the answer in the back of the book can be useful, but it is not sufficient because: 1) You will not always have "the back of the book". and 2) The solutions may be unreliable.
Other steps to be used as needed:
- Persist: If the problem doesn't work out the first ten times, try it again. If you persist long enough, you can solve most problems. Relatively few problems can be solved on the first try without a lot of experience.
- Do something else for a while: This is not a license to goof off. However, when working on a difficult problem doing something else for a while helps. While you are doing something else, either relaxing, working on a different subject, or whatever, your subconscious mind is churning. When you return to the problem you will often (not always) see something that you did not previously understand.
The copyright of the article Physics Homework Help in Physics is owned by Paul A. Heckert. Permission to republish Physics Homework Help in print or online must be granted by the author in writing.
