Calculus I · Unit 3B · review

Unit 3B Review: Applications of Integration

Unit 3B Review

Summary

Modeling questions to ask

• What small object or contribution am I adding? • What variable naturally locates that object? • What is its size, density, force, or distance factor? • What are the correct bounds? • Do the units of the integrand times the differential produce the desired units? • Does the sign have physical or geometric meaning?

Exercise

Find the area between y=2xy=2x and y=x2y=x^2 on 0x20\le x\le2 using vertical slices.

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Exercise 1 answer

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Exercise

Set up and evaluate the same area between y=2xy=2x and y=x2y=x^2 using horizontal slices.

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Exercise 2 answer

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Exercise

For the region between y=2xy=2x and y=x2y=x^2 on 0x20\le x\le2, find the volume about the xx-axis with washers and the volume about the yy-axis with shells. Compare how radius and height are defined.

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Exercise 3 answer

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Exercise

The base is the region under y=4x2y=\sqrt{4-x^2} above the xx-axis for 2x2-2\le x\le2. Cross-sections perpendicular to the xx-axis are semicircles whose diameters lie in the base. Find the volume.

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Exercise 4 answer

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Exercise

Find the arc length of y=2x+1y=2x+1 on [0,3][0,3], then verify the result with the distance formula between the endpoints.

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Exercise 5 answer

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Exercise

A rod occupies [0,3][0,3] and has density λ(x)=2+x\lambda(x)=2+x. Find its mass and center of mass.

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Exercise 6 answer

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Exercise

A spring has constant k=200N/mk=200\,\mathrm{N/m}. Find the work required to stretch it from 0.10m0.10\,\mathrm{m} to 0.30m0.30\,\mathrm{m} beyond equilibrium.

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Exercise 7 answer

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Exercise

A full conical tank is 4m4\,\mathrm{m} high with top radius 2m2\,\mathrm{m}. Water is pumped to an outlet 1m1\,\mathrm{m} above the top. Set up and evaluate the work using 9800N/m39800\,\mathrm{N/m^3}.

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Exercise 8 answer

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Exercise

A vertical rectangular plate is 2m2\,\mathrm{m} wide and extends from the water surface to a depth of 3m3\,\mathrm{m}. Find the hydrostatic force using 9800N/m39800\,\mathrm{N/m^3}.

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Exercise 9 answer

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Exercise

Marginal cost is C(q)=20+0.04qC'(q)=20+0.04q dollars per unit and C(100)=5000C(100)=5000. Find C(200)C(200) and identify the accumulated added cost.

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Exercise 10 answer

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After the explanation

Use the section idea

Reading lens

Mixed applications test modeling recognition: commit to a diagram and slice statement before looking for a familiar formula.

Mental model

A complete solution connects context, variable, bounds, slice contribution, integral, computation, units, interpretation, and a reasonableness check.

Decision

Classify the output and geometry first, solve from a blank start, then reveal one worked answer only to diagnose the earliest divergent decision.

Common trap

Reading a key before forming a setup or treating every wrong result as algebra when the real error was a radius, width, density, or bound.

Check yourself

Can you rebuild the setup without the answer open and defend every factor in a sentence?

Source & rights

Original instruction with traceable references.

BetterGrades-original; no direct adaptation declared in the verified handoff.

Reference textbooks remain rights-separated and are not published as application assets. Any direct adaptation requires separate identification and attribution.