Physics Sensei questions & answers
Why Do Physics Exam Questions Look Nothing Like the Homework?
You did every homework problem. Some twice. Then the exam starts, and the first problem is about a skier on a hill. You never did a skier problem. Panic.
Later, you look at the solution, and it’s the same physics as a homework problem about a box on a ramp. You just didn’t see it.
When physics exam questions look nothing like the homework, it’s usually not because the professor is being unfair. It’s because the exam changed the story, not the physics.
What’s really going on
Every physics problem has two layers. The surface is the story: a car, a skier, a box, an elevator. The deep layer is the physics: constant acceleration, energy, forces, momentum.
Professors write exams by keeping the deep layer and changing the surface. A skier sliding down a hill and a box sliding down a ramp are the same problem underneath.
If you learned to recognize problems by their surface, every new story looks like a new problem. If you learned to see the deep layer, the exam looks familiar.
Why homework makes it worse
Homework problems in a chapter often share the same surface too: ramp after ramp, car after car. So you start sorting problems by their story. “Oh, it’s a ramp problem.”
That works until the exam uses a story you haven’t seen. Then your sorting system has nothing to match.
Why it’s hard to change
The story is the first thing you see, and it’s vivid. Cars and skiers are easy to picture. The physics underneath is invisible until you look for it on purpose.
So you need a habit that looks past the story every time.
The fix: strip the story
Practice seeing the physics underneath by removing the story, then putting a new one on.
Try this on five homework problems: strip the story
- After you solve a problem, rewrite it in one line with no objects. Example: “Something starts from rest, speeds up at a constant rate, and I need the distance.”
- Name the big idea in that one line. Ask: What’s the big idea?
- Now invent a new story with the same physics. A car becomes a skateboard. A ramp becomes a hill.
- Solve your new version, notes closed. Ask: What are they asking? What do I know?
- On the next homework, read each problem and write the stripped line before you start.
What changes
After a few problems, you’ll catch yourself thinking, “This is just the ramp problem again,” even when there’s no ramp in sight.
On the exam, new stories stop being scary. You’ll read past the skier and see the physics you’ve already practiced.
Change the story, keep the physics. That’s what exams do. Practice it first.
Practice problems built for this
On Physics Sensei, every problem is solved step by step, and step three, “What’s the big idea?”, names the physics under the story. Practice sets include a problem where you have to spot the idea in a new situation. Each one asks you to try it first, and you find out right away exactly where you slipped.
Your next step: strip the story from three homework problems this week. Then try a practice set on Physics Sensei and spot the idea in the new situation.
More questions about studying and grades? See them all here.
Raul, Physics Sensei
