IEMJEE Physics preparation: Buoyancy and displaced fluid — worked example and reasoning

Problem to solve

Using g=10 m/s², a body displaces 0.003 m³ of water. Find buoyancy.

Try the problem before reading the answer. Record the requested quantity, relevant information and any interpretation choices. Keep this original practice example separate from official examination questions or previous-year papers.

Choose the governing principle

F_b=ρ_fluid g V_displaced.

The buoyant force equals the weight of fluid displaced, not generally the weight of the object.

Worked answer

1000×10×0.003=30 N upward.

The answer follows the stated model and the values in this question. Preserve exact expressions when given; if you use a numerical approximation, label it and keep sufficient precision until the final step.

Audit the reasoning

Check dimensions, direction and limiting behaviour. Ask whether the answer should increase or decrease when an input changes. A dimensional check is necessary in many calculations but cannot certify an omitted dimensionless coefficient or an inappropriate physical model.

A specific error to avoid here: For a submerged sinking object, buoyancy need not equal the object's weight.

Explain before repeating

Write a short explanation linking the governing principle to the answer rather than copying the final line. Identify one assumption and explain how violating it would make this method unreliable. Use the linked worksheet for a new task, then return to this example after a delay and solve it without the answer visible.

Official sources and verification

Sources checked on 26 October 2026. A source’s date, programme and campus limit which claims it supports. Official pages may change after review.

1. UEM — IEMJEE examination information

   Historical examination pattern; verify the current cycle on the central portal.

2. NTA — explicitly labelled JEE Main 2026 syllabus

   Historical PCM syllabus reference. Lessons and exercises are independently authored, not official IEMJEE papers or verified 2027 paper predictions.

3. NCERT — official textbook catalogue

   Primary textbook reference for checking school-level concepts. This directory does not certify the independent lesson or establish IEM examination weightage.

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