Some conceptual questions

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In summary, the conversation discusses conceptual questions related to acceleration and forces. It explores the acceleration of a rock thrown straight up, the effects of changing initial velocity components on maximum height, time of flight, and range, and the possible movement of an elevator based on a scale reading. The conversation also considers the effects of air resistance and differing forces on acceleration.
  • #1
mikefitz
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I was looking through my book tonight before my midterm exam and came across the following conceptual questions I would like to discuss before I take the test.

A rock is thrown straight up. It reaches the top of its path and starts to fall back down. It’s acceleration on the way down, neglecting air resistance, is:
(a) greater than when it was at the top of its path.
(b) the same as when it was at the top of its path.
(c) less than when it was at the top of its path.


Acceleration on the way down due to gravity would be 9.8m/s^2. However, couldn't the acceleration on the way up be greater than that? (IE: If I were to fire a bullet straight up it would have an acceleration greater than 9.8)

A ball is launched from ground level with initial velocity components vox and voy and flies through the air, reaching a maximum height, having a certain time of flight, and reaching a certain range. How will EACH of these 3 quantities change (increase/decrease/unchaged) if we increase vox (but keep voy at its original value)?

Maximum Height-- Time of Flight-- Range
(a) increase increase increase
(b) unchanged unchanged increase
(c) decrease decrease decrease
(d) increase unchanged unchanged
(e) decrease increase unchanged


Changing Vx wouldn only change the range since x/y components are independent, correct?



A passenger who weighs 180 lbs stands on a scale in an elevator. The scales read 190 lbs. The elevator could be
(a) moving upward and increasing its speed
(b) moving upward and decreasing its speed
(c) moving downward and increasing its speed
(d) moving downward at a constant speed


Probably moving upward and increasing in speed since there is a net force on the person greater than their weight.


Thoughts?
 
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  • #2
mikefitz said:
However, couldn't the acceleration on the way up be greater than that? (IE: If I were to fire a bullet straight up it would have an acceleration greater than 9.8)
Why - what forces are acting on it at this point?

Probably moving upward and increasing in speed since there is a net force on the person greater than their weight.
Thoughts?

If there is an apparent increase in mass, this means that they are acceerating upwards, or decelerating downwards. So really, there are two possibilities although your choice of 4 answers only includes 1 of them.
 
  • #3


Your reasoning for the first two questions is correct. The acceleration due to gravity is constant and is always 9.8m/s^2, regardless of the direction of motion. However, when the rock is thrown straight up, it is initially accelerating upwards and then decelerating as it reaches the top of its path. On the way down, it is accelerating downwards with a constant acceleration of 9.8m/s^2.

For the second question, you are correct that increasing the initial velocity in the x-direction would only affect the range and not the maximum height or time of flight. This is because the x and y components of motion are independent of each other.

In the last question, the passenger is experiencing a higher reading on the scale because of the upward acceleration of the elevator. This is due to the fact that the upward force from the elevator floor is greater than the downward force of the person's weight, resulting in a net upward force and a higher reading on the scale. So, the correct answer would be (a) moving upward and increasing its speed.
 

1. What is the difference between a concept and an idea?

A concept is a specific, well-defined thought or notion that can be used to understand or explain something. An idea is a more general and abstract thought or notion that may not have a clear definition. Concepts are often used to build upon and develop ideas.

2. How are concepts formed?

Concepts are formed through a combination of innate abilities and learned experiences. Our brains have the ability to categorize and organize information, which helps us form concepts. Concepts can also be influenced by cultural and societal norms.

3. Can concepts change over time?

Yes, concepts can change over time as our understanding and knowledge of the world evolves. New information and experiences can lead to a reevaluation and modification of existing concepts, or the formation of new ones.

4. What is the importance of concepts in scientific research?

Concepts are crucial in scientific research as they provide a framework for understanding and organizing data. They also help scientists to formulate hypotheses, design experiments, and interpret results. Without concepts, it would be difficult to make sense of the vast amount of information gathered through research.

5. How do concepts contribute to the development of theories?

Concepts play a key role in the development of theories by providing a foundation for understanding and explaining phenomena. Through the use of concepts, scientists can identify patterns and relationships between different observations, leading to the formation of theories that can be tested and refined through further research.

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