Worked solutions for physics and chemistry problems
Start with what's given and asked, name the law, keep units on every line, box the answer. How to explain physics and chemistry problems, and why it works.
By the Chasca team 6 min read
A good physics or chemistry solution starts with what is given and what is asked, names the law and why it applies, keeps the units on every line and ends on a boxed answer with a sensible number of significant figures. That order is what science teachers teach and exam markers reward, and it is exactly what a bare answer leaves out.
Why are science problems so often maths problems?
Because the exams are built that way. In England, the exam regulator Ofqual requires at least 30% of the marks in GCSE physics, 20% in chemistry and 10% in biology to assess mathematical skills; for A level physics, the minimum is 40%. And the working itself earns marks: Pearson Edexcel’s guide to its GCSE science exams says it awards marks for working, including substitution and rearrangement, and credits errors carried forward.
So a student who only learns the final number loses twice: once when they can’t reproduce the method, and again because the method is what the marker was looking for.
Why do students get stuck?
Often before the first line. In a classic 1981 study, Michelene Chi, Paul Feltovich and Robert Glaser asked physics experts and novices to sort problems. The novices grouped them by surface features, such as a ramp or a pulley, while the experts grouped them by the principle that solves them. A student who sees “ramp” instead of “Newton’s second law” doesn’t know where to start, which is why a good solution names the law and says why it applies.
Diagrams are the other half. In a two-year study of students in a physics course that used diagrams consistently, David Rosengrant, Alan Van Heuvelen and Eugenia Etkina found that students who drew a correct free-body diagram on an exam solved the problem correctly 85% of the time, while an incorrect diagram led to more wrong answers than drawing none.
How do students get help today?
From solution manuals that print the final answer, from tutors, and from video lessons that explain a topic but rarely the exact problem on the sheet. Tutoring costs climb just as science gets hardest: India’s 2025 national survey of school education found average spending on private coaching of ₹6,384 a student in higher secondary, against ₹525 in pre-primary. Language is the other barrier. The World Bank recommends teaching subjects beyond reading and writing in a student’s first language, so a solution should be explained in the language the student learns in, with the terms their teacher uses.
What should a worked science solution show?
Science teachers have names for the order. In a 2025 article on the Royal Society of Chemistry’s education site, Dan Beech and Paul Hesford recommend GUESS: Given, Units, Equation, Substitute, Solve. A video should follow the same order and add what a page can’t:
- Given and find, written as symbols with units (“m = 5 kg”), with the unknown marked.
- The law, and why it applies here, before any numbers.
- Units converted first, then the substitution with units written in.
- One step per line, each appearing as it is said.
- The answer with its unit, boxed, to a sensible number of significant figures, with a quick check that its size and unit make sense.
- The diagram drawn beside the working, part by part as each force, curve or row is named, so the eye isn’t split between two places. Drawing as you explain is one reason whiteboard videos work.
For chemistry, balancing goes element by element, counting atoms on both sides. For genetics, the path runs from the parents’ genotypes to their gametes, the Punnett square and the ratio.
What does that look like for one problem?
Take a 5 kg box resting on a ramp at 30° to the horizontal. Find the friction force that keeps it at rest.
- Given: m = 5 kg, θ = 30°, g = 9.8 m/s², and the box is at rest.
- Find: the friction force, f.
- The law: the box isn’t moving, so the forces along the slope balance. Friction holds back the part of the weight that pulls down the slope, so f = mg sin θ.
- Substitute: f = 5 × 9.8 × sin 30° = 5 × 9.8 × 0.5.
- Answer: f = 24.5 N, acting up the slope.
- Check: it’s less than the box’s full weight of 49 N, as it should be.
Beside the working, a free-body diagram shows the weight straight down, the normal force at right angles to the ramp and friction up the slope, each drawn as it is named.
What does the Science problems skill do?
We make Chasca, so weigh our part of this accordingly. The Science problems skill works physics and chemistry numericals, balancing, derivations and genetics crosses on a teacher’s board:
- Bring the problems typed or pasted, or as photos, a PDF or a document of the sheet, up to 20 pages, with options and your key if they have them.
- The board opens with “Given:” and “Find:” in the video’s language, such as दिया है in Hindi, المعطيات in Arabic or Datos in Spanish.
- The narrator names the law and why it applies, converts units first, substitutes with units and ends on the answer with its unit and sensible significant figures, boxed, then checks it.
- A diagram is drawn beside the working when one helps: a free-body diagram with each force pointing the way it really acts, a motion graph, a data table, a Punnett square, a probability or pedigree tree, or a ramp or lens set-up drawn as lines. Each part appears as it is named.
- Every answer is solved a second time, separately, before the video is drawn. If anything disagrees, or disagrees with your key, the video’s page tells you which question to check.
- The narration is worded the way science teachers of your language explain, in any of 30 narrators or your own voice, with captions that never run ahead of the voice. Arabic is laid out right to left.
Who is it for?
Physics and chemistry teachers who want a worked solution for every question on a worksheet, tutors and coaching centres building problem sets for school-leaving and entrance exams, and channels that publish solved numericals in Hindi, Arabic, Spanish and other languages.
What won’t it do?
- Draw circuits or lab apparatus yet. Those questions are worked without a diagram.
- Guess an answer it can’t check. A disagreement is shown to you, never hidden.
- Replace practicals or practice. It explains a solution; students still need to solve the next problem themselves.
How do you make one?
- Open Science problems in Chasca and type or paste the problems, or add photos or a PDF of the sheet.
- Add the options and your key if the problems have them, and say the level or exam if you want problems written for you.
- Pick the language, the voice and a black board or whiteboard, then make the video.
- Check the video’s page for any flagged question before you share it.
Your first two videos are free, up to a minute each, watermarked and with no card required; a free video works the first problems that fit in its minute. Plans start at $9.99 a month (pricing).
Sources
- Ofqual (2015). GCSE reform: regulations for science.
- Ofqual (2016). GCE Subject Level Conditions and Requirements for Science (Biology, Chemistry, Physics).
- Pearson Edexcel. Understanding our exams: GCSE Sciences.
- Chi, M. T. H., Feltovich, P. J., & Glaser, R. (1981). Categorization and representation of physics problems by experts and novices. Cognitive Science, 5(2), 121–152.
- Rosengrant, D., Van Heuvelen, A., & Etkina, E. (2009). Do students use and understand free-body diagrams? Physical Review Special Topics: Physics Education Research, 5, 010108.
- Ministry of Statistics and Programme Implementation, Government of India (2025). Results of Comprehensive Modular Survey: Education, 2025.
- World Bank (2021). Teaching young children in the language they speak at home is essential to eliminate Learning Poverty.
- Beech, D., & Hesford, P. (2025). Success with GUESS for solving equation-based problems. RSC Education.
Video transcript What the narrator says in the 2:11 explainer above.
In this video, we calculate the horizontal range and maximum height of a kicked ball.
Question one. A ball is kicked at twenty metres per second at forty-five degrees to the ground. How far does it travel before it lands, and how high does it go? G equals nine point eight metres per second squared.
Assume the ball lands at its launch height and air resistance is negligible. The initial speed is twenty metres per second, and the launch angle is forty-five degrees. The downward acceleration is nine point eight metres per second squared.
You need the horizontal range and the maximum height above the launch point.
First, resolve the initial velocity into horizontal and vertical components using cosine and sine. The horizontal component is twenty times cosine forty-five degrees, giving ten root two metres per second. The vertical component is twenty times sine forty-five degrees, also giving ten root two metres per second.
Because launch and landing heights match, the total flight time is twice the initial vertical component divided by g.
Substituting twice ten root two metres per second over nine point eight metres per second squared gives two point eight eight six seconds.
Horizontal velocity stays constant, so the range is horizontal velocity multiplied by flight time.
Multiplying ten root two metres per second by two point eight eight six seconds gives forty point eight metres. At maximum height, vertical velocity is zero, so the height is the initial vertical component squared divided by twice g.
Substitute ten root two metres per second squared, divided by nineteen point six metres per second squared.
The maximum height is ten point two metres. As a check, at forty-five degrees the range should be four times the maximum height, which these values satisfy.
Hence, the ball travels forty point eight metres horizontally and rises ten point two metres above its launch point.
Questions people ask
List what is given, with units, and what you need to find; name the law that links them and why it applies; convert units, substitute and solve; then box the answer with its unit and check that its size makes sense.
GUESS stands for Given, Units, Equation, Substitute, Solve: a checklist for equation-based problems recommended in a 2025 article on the Royal Society of Chemistry's education site. It stops students skipping unit conversions and rearranging.
Because the marks are in the method as well as the answer. In England, at least 30% of GCSE physics marks assess mathematical skills, and Pearson Edexcel awards marks for working such as substitution and rearrangement.
Yes. In a two-year study, students who drew a correct free-body diagram on an exam solved the problem correctly 85% of the time, while an incorrect diagram led to more wrong answers than drawing none.
Yes. The Science problems skill draws free-body diagrams, motion graphs, data tables, Punnett squares and probability trees beside the working, part by part as each is named. It doesn't draw circuits or lab apparatus yet.
Yes. The narration is worded the way science teachers of that language explain, the board's Given and Find lines are written in that language, and Arabic is laid out right to left.
