RRB ALP Basic Science Practice: Units, Formulas and Three Worked Numerical Checks

Practise RRB ALP science numericals with unit conversions, electricity and motion examples, then use an error log to catch formula and substitution mistakes.

A memorised formula is useful only if you choose the right quantities and keep their units consistent. RRB ALP preparation benefits from a repeatable numerical routine: identify the quantity, convert the units, choose the relationship, substitute and check the result.

The examples below are original learning exercises, not official previous-year questions or a complete syllabus. Refer to the official RRB ALP CEN 01/2025 notice for that historical cycle and the RRB Chandigarh notice board for the applicable notice. Do not treat ALP and Technician requirements as interchangeable simply because a practice bundle includes both labels.

Build a quantity-first formula sheet

Instead of writing only “P = VI”, add what every symbol means, its SI unit and the conditions under which you are using the relationship.

Symbols can vary across books. Read the question definition rather than assuming every letter always means the same thing. Match each practice topic to your official syllabus before adding it to your revision list.

Worked example 1: Speed conversion before distance

Question: A vehicle moves at a constant 72 km/h for 15 seconds. How far does it travel?

First convert the speed: 72 × 1000 / 3600 = 20 m/s. Then use distance = speed × time: 20 m/s × 15 s = 300 m.

The seconds cancel, leaving metres. A quick independent check is 72 × 5/18 = 20 m/s. At 20 metres each second, 15 seconds should produce a few hundred metres, not several kilometres.

Common mistake: Multiplying 72 by 15 and calling the result metres. The number 72 was expressed per hour, while 15 was expressed in seconds. The arithmetic alone is not the problem; the unmatched units are.

Transfer exercise: At 54 km/h, the same vehicle travels for 12 seconds at constant speed. The conversion gives 15 m/s and the distance is 180 m.

Worked example 2: Current, power and energy are different

Question: An ideal 6-ohm resistor is connected across a constant 12-volt supply. Find its current, power and energy used in two minutes.

Using Ohm’s law for this ideal ohmic resistor, I = V/R = 12/6 = 2 A. Power is P = VI = 12 × 2 = 24 W. Convert two minutes to 120 seconds; energy is E = Pt = 24 × 120 = 2,880 J.

Cross-check the power with V²/R: 144/6 = 24 W. The energy unit follows from watt-seconds, which are joules.

Common mistake: Writing 24 joules for the power or using two as the time in an SI calculation. Power describes the rate of energy transfer; energy depends on how long that transfer continues. The example assumes constant voltage and resistance; it is not a claim that all real devices behave as ideal resistors.

Worked example 3: State the motion assumption

Question: A body starts from rest and accelerates uniformly at 2 m/s² for five seconds. Find its final speed and displacement.

With initial speed u = 0, final speed v = u + at = 0 + 2 × 5 = 10 m/s. Displacement s = ut + ½at² = 0 + ½ × 2 × 25 = 25 m.

For constant acceleration, average speed here is (0 + 10)/2 = 5 m/s. Multiplying by five seconds also gives 25 m. That provides a second route to check the displacement.

Common mistake: Using final speed × time, which gives 50 m and assumes the body travelled at 10 m/s throughout. It did not: it increased from rest to that speed.

Review the failure stage, not just the answer

Use four labels in your numerical error log: concept, formula selection, unit conversion and calculation. If the formula was right but minutes were left unconverted, rereading the entire chapter is unlikely to be the most targeted repair. Practise several unit conversions, then revisit a mixed question.

Try a short session with one concept question, three numerical exercises and a final check of units and assumptions. Gradually combine topics once individual steps become dependable. Use the RRB ALP Test Series and read each test’s details to confirm stage and subject coverage.

Frequently asked questions

Can dimensional checking prove that my answer is correct?

No. It can reveal a mismatch, such as reporting speed in metres, but a dimensionally consistent answer can still contain a wrong formula, assumption or number.

Should I use a calculator during practice?

For exam simulation, follow the tools permitted in the applicable official instructions. During learning, an independent calculation can help check arithmetic, but do not make your timed routine depend on an unpermitted tool.

Is a formula sheet enough for Basic Science and Engineering?

No. Include conceptual understanding and the other topics in your applicable syllabus. These three exercises demonstrate a method, not comprehensive coverage.

Put the routine into timed practice

Explore Scholareum mock tests, review chapter-wise versus full-length tests, and use mock-test analysis to choose your next repair session. Check dates and official links through the exam calendar, confirming all cycle-specific requirements against the recruiting body’s notice.