Question

Which statement is true about a parabolic dish? (1 point)
Responses

It refracts waves in the dish.
It refracts waves in the dish.

It absorbs the wave energy.
It absorbs the wave energy.

It reflects waves and focuses them to a point.
It reflects waves and focuses them to a point.

It filters the type of electromagnetic radiation

Which natural phenomenon describes guitar strings vibrating at certain natural frequencies?



Source:giphy

(1 point)
Responses

beats
beats

resonance
resonance

oscillation
oscillation

interference
interference
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Question
A machine works with an efficiency of 18%. The energy input is 500 joules/second. How much useful energy will the machine generate in 15 minutes?(1 point)
Responses

25 kJ
25 kJ

1.35 kJ
1.35 kJ

135 kJ
135 kJ

81 kJ
81 kJ
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Question
What will increase the power output when doing work? Click all that apply.(2 points)
Responses

doing less work and increasing the amount of time
doing less work and increasing the amount of time

doing more work in the same amount of time
doing more work in the same amount of time

doing the same amount of work in less time
doing the same amount of work in less time

doing the same work and more time
doing the same work and more time
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Question
Match the written descriptions of the energy changes to the technology it describes. You have 2 tries.(4 points)
Put responses in the correct input to answer the question. Select a response, navigate to the desired input and insert the response. Responses can be selected and inserted using the space bar, enter key, left mouse button or touchpad. Responses can also be moved by dragging with a mouse.
Converts electrical current to electromagnetic waves and vice versa Converts sound to electrical current Converts electrical signals to sound and then sound back to electrical signals Converts solar energy to electrical energy
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Answer 1

Let's break down each question and provide the correct answers:

1. **Which statement is true about a parabolic dish?**
- **Response:** It reflects waves and focuses them to a point.

2. **Which natural phenomenon describes guitar strings vibrating at certain natural frequencies?**
- **Response:** resonance

3. **A machine works with an efficiency of 18%. The energy input is 500 joules/second. How much useful energy will the machine generate in 15 minutes?**
- First, calculate the total energy input over 15 minutes:
\[
500 \text{ joules/second} \times 900 \text{ seconds} = 450,000 \text{ joules} = 450 \text{ kJ}
\]
- Now calculate the useful energy using the efficiency:
\[
\text{Useful Energy} = 450 \text{ kJ} \times 0.18 = 81 \text{ kJ}
\]
- **Response:** 81 kJ

4. **What will increase the power output when doing work? Click all that apply.**
- **Responses:**
- doing more work in the same amount of time
- doing the same amount of work in less time

5. **Match the written descriptions of the energy changes to the technology it describes.**
Here are the appropriate descriptions matched:
- **Converts electrical current to electromagnetic waves and vice versa:** Radio transmitter/receiver
- **Converts sound to electrical current:** Microphone
- **Converts electrical signals to sound and then sound back to electrical signals:** Telephone
- **Converts solar energy to electrical energy:** Solar panel

Feel free to ask if you need more help with your questions!