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What is a variable? How do you distinguish a dependent variable from an independent one in a problem?

Short Answer

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Question: Define variable and explain the difference between dependent and independent variables in a problem. Answer: A variable is a symbol, usually represented by a letter, that can take on different values in a mathematical equation, function, or model. It is used to represent an unknown quantity or a changing quantity that depends on other variables. Dependent variables are variables whose values depend on the values of other variables in the problem, often representing the outcome or response. Independent variables, on the other hand, do not depend on the value of other variables in the problem and generally represent the factors that influence the dependent variables or cause the outcome. To distinguish between dependent and independent variables in a problem, identify which variables have values determined by other variables and look for the cause-and-effect relationship between them.

Step by step solution

01

Definition of a Variable

A variable is a symbol, usually represented by a letter, that can take on different values in a mathematical equation, function, or model. It is used to represent an unknown quantity or a changing quantity that depends on other variables.
02

Dependent Variables

A dependent variable is a variable whose value depends on the value of other variables in the problem. In a mathematical function or equation, it is the output variable, which means that its value is determined by the values of the input variables.
03

Independent Variables

An independent variable is a variable that does not depend on the value of other variables in the problem. In a function or equation, it is the input variable, which means that its value determines the value(s) of other dependent variables.
04

Distinguishing Dependent from Independent Variables in a Problem

In order to distinguish dependent variables from independent ones in a problem, it's important to identify which variables have values that are determined by the values of other variables and which ones do not. Look for the cause-and-effect relationship between the variables. Generally, the dependent variables represent the "effect" (the outcome or the response), and the independent variables represent the "cause" (the factors that influence the outcome).

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Most popular questions from this chapter

Liquid water flows in a tube with the inner surface lined with polyvinylidene chloride (PVDC). The inner diameter of the tube is \(24 \mathrm{~mm}\), and its wall thickness is \(5 \mathrm{~mm}\). The thermal conductivity of the tube wall is \(15 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}\). The water flowing in the tube has a temperature of \(20^{\circ} \mathrm{C}\), and the convection heat transfer coefficient with the inner tube surface is $50 \mathrm{~W} / \mathrm{m}^{2}\(. \)\mathrm{K}$. The outer surface of the tube is subjected to a uniform heat flux of \(2300 \mathrm{~W} / \mathrm{m}^{2}\). According to the ASME Code for Process Piping (ASME B31.3-2014, \(\mathrm{A} .323\) ), the recommended maximum temperature for PVDC lining is \(79^{\circ} \mathrm{C}\). Formulate the temperature profile in the tube wall. Use the temperature profile to determine if the tube inner surface is in compliance with the ASME Code for Process Piping.

A heating cable is embedded in a concrete slab for snow melting on a $30 \mathrm{~m}^{2}$ surface area. The heating cable is heated electrically with joule heating. When the surface is covered with snow, the heat generated from the heating cable can melt snow at a rate of \(0.1 \mathrm{~kg} / \mathrm{s}\). According to the National Electrical Code (NFPA 70), the power density for embedded snow-melting equipment should not exceed $1300 \mathrm{~W} / \mathrm{m}^{2}$. Formulate the temperature profile in the concrete slab in terms of the snow melt rate. Determine whether melting snow at $0.1 \mathrm{~kg} / \mathrm{s}$ would be in compliance with the NFPA 70 code.

Consider a large plane wall of thickness \(L=0.8 \mathrm{ft}\) and thermal conductivity $k=1.2 \mathrm{Btu} / \mathrm{h} \cdot \mathrm{ft} \cdot{ }^{\circ} \mathrm{F}$. The wall is covered with a material that has an emissivity of \(\varepsilon=0.80\) and a solar absorptivity of \(\alpha=0.60\). The inner surface of the wall is maintained at \(T_{1}=520 \mathrm{R}\) at all times, while the outer surface is exposed to solar radiation that is incident at a rate of $\dot{q}_{\text {solar }}=300 \mathrm{Btu} / \mathrm{h} \cdot \mathrm{ft}^{2}$. The outer surface is also losing heat by radiation to deep space at \(0 \mathrm{~K}\). Determine the temperature of the outer surface of the wall and the rate of heat transfer through the wall when steady operating conditions are reached. Answers: $554 \mathrm{R}, 50.9 \mathrm{Btu} / \mathrm{h}^{\mathrm{ft}}{ }^{2}$

A heating cable is embedded in a concrete slab for snow melting. The heating cable is heated electrically with joule heating to provide the concrete slab with a uniform heat of \(1200 \mathrm{~W} / \mathrm{m}^{2}\). The concrete has a thermal conductivity of \(1.4 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}\). To minimize thermal stress in the concrete, the temperature difference between the heater surface \(\left(T_{1}\right)\) and the slab surface \(\left(T_{2}\right)\) should not exceed \(21^{\circ} \mathrm{C}\) (2015 ASHRAE Handbook-HVAC Applications, Chap. 51). Formulate the temperature profile in the concrete slab, and determine the thickness of the concrete slab \((L)\) so that \(T_{1}-\) \(T_{2} \leq 21^{\circ} \mathrm{C}\).

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