How to Study Physics When You Understand the Lecture but Blank on Problems

The professor works through a problem on the board. A block slides down a ramp, friction, a pulley, the whole thing. Every step makes sense. You nod along, copy it down, and think "OK, I get this."

Then you open the problem set that night. Different block, different ramp. And you have no idea where to start.

If that's your physics class, you're in very normal company. Following a solution and producing one are different skills, and most physics studying only trains the first one. This post is about how to study physics so you build the second one, the one the exam actually tests.

Why physics is uniquely hard to study

Physics punishes the study habits that get you through other classes.

In history or biology, you can do reasonably well by knowing the content. In physics, knowing the content is only the start. You also have to recognise which principle a problem is about (it rarely says), set it up correctly, and then carry the math through without dropping a sign. A problem can fail at any of those three points, and rereading your notes only practices the first.

There's also a specific trap. In 1981 Michelene Chi, Paul Feltovich and Robert Glaser asked physics experts and novices to sort physics problems into groups. The novices grouped them by surface details, like which objects appeared in the problem. The experts grouped them by the principle needed to solve them, like conservation of energy or Newton's second law. Their results showed that how you categorise a problem at the start shapes how you go on to set it up and solve it.

So when a new problem "looks different" from the one in lecture, that's often because you're seeing the ramp and the pulley. The expert sees an energy problem. Same page, different problem.

And then there's the worked example trap. Watching someone solve a problem gives you a strong sense of understanding. That feeling is real, but it's a feeling about the example, not about your ability to solve the next one. It's the illusion of competence in its physics form.

How to study physics problems: the method

1. Name the principle before you touch the math

For every problem you study, worked example or homework, start by writing one line at the top: "This is a ___ problem because ___."

"This is a conservation of energy problem because nothing is doing work except gravity and I know the start and end heights." "This is a Newton's second law problem because they want the acceleration and I can list the forces."

It feels slow at first. That's the point. You're training the expert habit from the Chi study, sorting by principle instead of by what the picture looks like. After a couple of weeks you'll notice you can do it in seconds, and that's when new problems stop looking foreign.

2. Explain every step of worked examples to yourself

When you study a worked example from lecture or the textbook, don't read it. Interrogate it. At each line, say why that step happened. Where did this equation come from? Why did they choose this direction as positive? What would change if the ramp had no friction?

This comes from another Michelene Chi study, from 1989, which looked at students learning mechanics from worked examples. The students who went on to solve problems well were the ones who explained the examples to themselves as they went and noticed when they didn't understand something. The weaker students read the examples and then relied on copying them. We covered that study and the method properly in the post on the self-explanation effect, so I won't repeat it here. For physics, if you can't say why a line is there, you don't understand that line yet.

3. Fade the example, one step at a time

This is the bridge between "I understand the example" and "I can do the problem."

Take a worked example you've already self-explained. Cover the last step and do it yourself. Next time, cover the last two steps. Then the last three. Keep going until you're starting from the problem statement with nothing but the principle you named.

Researchers call this fading. In a 2002 paper in The Journal of Experimental Education, Alexander Renkl, Robert Atkinson and colleagues compared fading against the usual approach of studying an example and then trying a matching problem. One of their experiments used a physics lesson on electricity. Students who learned with faded examples did better on problems similar to the ones they practiced, and they made fewer errors along the way.

You don't need special materials for this. A sticky note or a sheet of paper over the solution does the job.

4. Solve cold, then check

Once you can finish a faded example from the start, switch to fresh problems. No notes open, no solution peeking, no scrolling back through the lecture slides.

Give each problem a real attempt, at least 10 minutes if you're stuck, before you look anything up. When you do look, look for the smallest hint that gets you moving (usually the principle), then close it and keep going. A problem you solved with one hint teaches you far more than one you "solved" by reading the solution.

Honestly, this is the part that feels worst. Struggling on a problem you can't solve yet feels like failing. It's the practice the exam is going to demand.

5. Mix your problem sets

Textbook problem sets are usually blocked. Chapter 5 problems are all chapter 5, so you know the principle before you read the question. The exam won't do you that favor.

Once you've got a few chapters behind you, mix them. Take two problems each from kinematics, forces and energy, shuffle them, and solve them in random order. Now you have to decide which principle applies, which is the exact skill from step 1.

The evidence for this is strong in math, which is the closest match to physics problem-solving that's been tested this way. In a 2015 classroom study, Doug Rohrer, Robert Dedrick and Sandra Stershic had 126 seventh graders practice with either blocked or mixed (interleaved) problem sets over several months. On a surprise test 30 days after a review session, the mixed group scored 74 percent and the blocked group scored 42 percent. The interleaved practice guide has more on setting this up.

It'll feel harder than blocked practice. That's expected, and it doesn't mean it's working worse.

6. Keep a mistakes page

Every time you get a problem wrong, write one line about why. Not "calculation error" but the actual cause. "Forgot the normal force isn't mg on a ramp." "Used the wrong sign for work done by friction." "Didn't convert grams to kilograms."

After a few weeks, patterns show up. You'll probably find three or four mistakes you make over and over. Those go on a card you read before every exam. The math study guide has a longer version of this idea if you want it.

A weekly physics study workflow

Here's what this looks like in a normal week with two lectures and a problem set due Friday.

After each lecture (30 minutes): pick one worked example from class. Name the principle, then self-explain every line.

Two days later (30 to 45 minutes): fade that example. Cover the second half and work it yourself. If that goes fine, cover more.

Problem set (spread over two or three evenings): solve cold. Attempt every problem properly before you use hints. Log every mistake on your mistakes page.

Weekend (45 minutes): mixed review. Six problems pulled from this week and earlier chapters, shuffled. No notes. Check, then log mistakes.

Before the exam: a timed mixed set, your mistakes page, and nothing that involves rereading solutions.

That's about four hours a week on top of lectures. If that sounds like a lot, compare it with the hours you already spend rereading notes and watching solution videos. This moves that time onto the parts the exam actually tests.

FAQ

Why do I understand physics in class but can't do the problems?

Following a solution and producing one use different skills. Lectures show you finished reasoning, so they build recognition, not the ability to choose a principle and set up a problem from scratch. You build that by solving problems without the solution in front of you.

How many physics problems should I do to study for an exam?

There's no magic number, but quality beats volume. Ten problems solved cold, with the principle named and mistakes logged, will do more than thirty where you glanced at the solution when you got stuck. Make sure at least some of them are mixed across chapters.

Is it bad to look at the solution when I'm stuck?

Not if you do it carefully. Give the problem a real attempt first, then look only far enough to get unstuck, usually just the principle or the first step. Close the solution and finish on your own. Then try a similar problem later without any help.

Should I memorize physics formulas?

Know the core ones well enough that you don't have to hunt for them, and flashcards are fine for that. But plenty of students who struggle on physics exams know the formulas. What they can't do is pick the right one. Spend most of your time on steps 1 and 5, choosing and mixing.

Does watching physics videos help?

Videos are worked examples, so they help the same way lectures do. They build understanding of one solution. Treat them like any worked example: pause, predict the next step, and then fade it later.

Try it on one problem tonight

Open your notes from the last lecture and find the worked example that felt easiest. Write "This is a ___ problem because ___" at the top. Then cover the second half and finish it yourself. If you can, great, try a problem from the set cold. If you can't, you've just found exactly what to study tomorrow.

For the mixed review sessions, StudyLab can turn your lecture PDFs into quizzes, which is a quick way to practice naming the principle behind a problem before you start solving.