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Ch. 6 - Applications of Integration
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243당신이 사용하는 게 아니라요?교과서 변경
6장, 문제 6.7.34

Leaky Bucket A 1-kg bucket resting on the ground contains 3 kg of water. How much work is required to raise the bucket vertically a distance of 10 m if water leaks out of the bucket at a constant rate of 1/5 kg/m? Assume the weight of the rope used to raise the bucket is negligible. (Hint: Use the definition of work, W = ∫a^bF(y) dy, where F is the variable force required to lift an object along a vertical line from y=a to y=b.)

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1
Identify the variable force function F(y) that represents the weight of the bucket plus the remaining water at height y. Since water leaks at a constant rate of \( \frac{1}{5} \) kg per meter, the mass of water at height y is \( m(y) = 3 - \frac{1}{5}y \) kg. The total mass being lifted at height y is then \( 1 + m(y) = 1 + 3 - \frac{1}{5}y = 4 - \frac{1}{5}y \) kg.
Express the force F(y) as the weight of the bucket plus water at height y. Since weight is mass times gravitational acceleration \( g \), we have \( F(y) = (4 - \frac{1}{5}y) \times 9.8 \) newtons.
Set up the integral for work using the formula \( W = \int_a^b F(y) \, dy \), where \( a = 0 \) m (starting height) and \( b = 10 \) m (final height). So, \( W = \int_0^{10} (4 - \frac{1}{5}y) \times 9.8 \, dy \).
Simplify the integral by factoring out constants and rewriting the integrand: \( W = 9.8 \int_0^{10} \left(4 - \frac{1}{5}y\right) dy \).
Evaluate the integral by integrating term-by-term: \( \int_0^{10} 4 \, dy \) and \( \int_0^{10} \frac{1}{5}y \, dy \), then multiply the result by 9.8 to find the total work done in lifting the bucket and leaking water.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Work as an Integral of Variable Force

Work done by a variable force is calculated using the integral W = ∫ F(y) dy, where F(y) changes with position y. This approach sums infinitesimal amounts of work over the distance, accounting for forces that vary as the object moves.
추천 영상:
가이드 코스
06:22
Introduction To Work

Force Due to Weight and Variable Mass

The force required to lift an object vertically equals its weight, which depends on mass and gravity (F = mg). When mass changes with height, as water leaks out, the force becomes a function of position, requiring careful modeling of mass variation.
추천 영상:
가이드 코스
09:32
Lifting Problems

Modeling Mass Loss as a Function of Height

When water leaks at a constant rate per meter, the mass decreases linearly with height. Expressing mass as a function of vertical position allows calculation of the changing force and integration over the lifting distance.
추천 영상:
가이드 코스
09:32
Lifting Problems
관련 실천
교과서 질문

Assume f and g are continuous, with f(x) ≥ g(x) ≥ 0 on [a, b]. The region bounded by the graphs of f and g and the lines x=a and x=b is revolved about the y-axis. Write the integral given by the shell method that equals the volume of the resulting solid.

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교과서 질문

9–20. Arc length calculations Find the arc length of the following curves on the given interval.

y = −8x−3 on [−2, 6] (Use calculus.)

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교과서 질문

9–12. Consider the cylindrical tank in Example 4 that has a height of 10 m and a radius of 5 m. Recall that if the tank is full of water, then ∫₀¹⁰ 25 π ρg(15−y) dy equals the work required to pump all the water out of the tank, through an outflow pipe that is 15 m above the bottom of the tank. Revise this work integral for the following scenarios. (Do not evaluate the integrals.)


The work required to empty the top half of the tank

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교과서 질문

For the following regions R, determine which is greater—the volume of the solid generated when R is revolved about the x-axis or about the y-axis.


R is bounded by y=1−x^3, the x-axis, and the y-axis.

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교과서 질문

Let R be the region bounded by the following curves. Find the volume of the solid generated when R is revolved about the given line.


x=2−secy,x=2,y=π/3, and y=0; about x=2

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교과서 질문

Let f(x) = {x   if 0≤x≤2

      2x−2  if 2<x≤5

      −2x+18 if 5<x≤6. 


Find the volume of the solid formed when the region bounded by the graph of f, the x-axis, and the line x=6 is revolved about the x-axis.

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