Activity 1.2.5 Mechanical System Efficiency Answer Key

IntroductionEnergy cannot be created or destroyed, but energy can be converted from one form to another. By design, an engineer creates an energy conversion system to change an input energy form into a desired output energy form. However, within a conversion system, input energy can be changed into less desirable forms of energy. Less desirable forms of energy conversion can occur due to resistance and friction, resulting in thermo energy conversion. Engineers strive to decrease undesirable energy conversions within a system, or energy losses, by planning with system efficiency in mind. Efficiency is the ratio of desired output energy compared to input energy.

A common form of energy conversion today occurs through electromagnetic induction. Electromagnetic induction transfers mechanical energy into electrical energy. The electrical energy is then transmitted to industries and homes to be used in a variety of ways, many of which include conversion back to mechanical energy.

Equipment Calculator

ProcedureIn this activity you will investigate an energy conversion system designed to change electrical energy into mechanical energy. Given ATV (All-Terrain Vehicle) winch data, you will determine the efficiency of the system under various loads. Remember units and precision when recording data.

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POE – Unit 1 – Lesson 1.2 – Activity 1.2.5 – Mechanical System Efficiency Answer Key – Page 1

ATV Winch Data

ATV winches pull a horizontal load during testing. The winch pulls a weight where the friction produces a force which is measured as tension in the cable. The following data can be used to compare electrical input to mechanical output to determine system efficiency.

Force Distance Time Current Volts0 24 m 180 s 15 A 12 V7000 N 24 m 360 s 100 A 12 V11000 N 24 m 720 s 160 A 12 V

Work involves the amount of force (F) exerted over a specific distance (D). Note that work is not related to time. For example running up a flight of stairs in four seconds requires a different level of exertion than if you walk up a flight of stairs in thirty seconds. You will feel differently in each scenario even though you did the same amount of work. Use the following formula to determine how many joules (J) of work it took to lift the weight in the system. As you carry your units through to the solution, change the final answer from Nm to J.

1. Determine the work done by the winch system for each test.

Formula Substitute / Solve Final Answer (0)

Work = (F)(D) = (N)(m)

(0)(24m) = 0Work = 0

(7000N)(24m) = 168,000 N-m or J Work = 168,000 J

(11000N)(24m) = 168,000 N-m or J Work = 264,000 J

Power involves time, force, and distance. In the previous example, the same amount of work was done regardless of time. To climb the stairs more quickly, a person needs more power. Use the formula below to calculate the output power of the system in watts (W). As you carry your units through to the solution, change the final answer from J/s to W.

2. Determine the output power of the system for each test. Your final answer will be in watts.

Formula Substitute / Solve Final Answer (0.0)

A. Pout = 0.0 W

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out

Work JP

Time s

Pout = 466.7 W

Pout = 366.7 W

3. To calculate power of an electrical system, multiply the current and voltage. Substitute and solve to discover how many watts were put into your system. You do not need to show the relationship of units to solve the problem, but be sure to label your final answer as watts.

Formula Substitute / Solve Final Answer(0)

Pin = (I)(V)

(15A)(12V) = 180 W Pin = 180 W

(100A)(12V) = 180 W Pin = 1200 W

(160A)(12V) = 180 W Pin = 1920 W

4. In order to compare the energy input versus the output, the efficiency of the system must be determined. Use the given formula to calculate efficiency.

Formula Substitute / Solve Final Answer(0)

Pin = (I)(V)

% Efficiency = 0.0

% Efficiency = 38.9%

% Efficiency = 19.1%

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Conclusion1. Which scenario is most efficient? What factors make one scenario more efficient

than another?

The 7000 N pull test is most efficient. Answers will vary. A possible answer is heating of components under high load may decrease motor efficiency. Another is that friction with the motor may increase significantly as the load increases.

2. Describe at least one strategy for making this system more efficient.

Answers will vary. An example is to test and improve subcomponents and then add subsystems to a final assembly.

3. Explain at least two reasons why automotive engineers are concerned with improving vehicle efficiency.

Answers will vary. Examples include improving fuel efficiency, reducing component wear, and reducing emissions.

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