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How much time does it take for nuclear radiation from a bomb to decay to a safe level? —Preceding unsigned comment added by Cborgen ( talk • contribs) 00:05, 16 December 2009 (UTC)
From an article about a recently re-analyzed black hole - The outermost layers of the star are being siphoned by the black hole. The swirling gas forms a hot plasma disk around the black hole before it disappears, and the process emits a lot of X-rays and radio waves. The part in bold, can we observe that in motion? If Hubble takes a look at that pair and then looks back a day later - can we see a change? a week/month/year later? It's easy for me to visualize swirling masses of plasma being sucked off/out of a star and into the black hole, but I'm VERY curious about the timescales involved. Surely observation of the process-in-motion is possible with instruments, it being only a question of resolution? Are we there yet? Can we watch this happening or is it still the "snapshot" approach? 218.25.32.210 ( talk) 08:05, 16 December 2009 (UTC)
Hello. How is the main product of the condensation between propanoic acid and 3-aminopropanal named according to IUPAC nomenclature? I think that the aldehyde group in 3-aminopropanal does not react and naming the main product 3-formyl-N-propylpropanamide is ambiguous since the aldehyde group can be on the alkyl chain or the 'amide' chain by the naming alone. Is the main product a double-branched amine or a single-branched amide? Thanks in advance. -- Mayfare ( talk) 09:15, 16 December 2009 (UTC)
If you gathered all the insects in the world together, how much would they weigh in total? -- OpenToppedBus - Talk to the driver 11:47, 16 December 2009 (UTC)
why are atoms colourless, despite colour originally containing atoms has colour?
colour or paint is made from various compounds.Molecules combine to form compounds.a moleculeis formed by the combination of atoms.As we know that atom retains its identity throughout chemical change.therefore atoms should have colour —Preceding unsigned comment added by Omkar2510 ( talk • contribs) 12:54, 16 December 2009 (UTC)
See
HOMO-LUMO gap. The colour behaviour of a substance is determined by its chemical environment, e.g. electron charge density and the relative energies of various electronic orbitals.
John Riemann Soong (
talk)
18:57, 17 December 2009 (UTC)
In a combination of serial and parallel circuits, such as this one, am I correct to conclude that all three lamps shine equally brightly? My reasoning is that a and b/c are connected serially, so both a and b/c should get half of the voltage of the cell. B and c are connected in parallel, so they each get the full amount, thus all three each get half of the voltage of the cell. (I know this might sound like homework, but I am just trying to understand more about electricity and I have no teacher whom I can ask...) Lova Falk ( talk) 14:41, 16 December 2009 (UTC)
I have questions after reading http://news.bbc.co.uk/2/hi/science/nature/8414476.stm but don't know where to look in Wikipedia. (1) On a planet five time the mass of earth, what would the gravity be like? What would it be like to walk on the surface? (2) What are the odds of any given planetary atmosphere being breathable by humans? (3) How long would it take to travel to a planet 28 light years away using current technology? Thank you for helping. —Preceding unsigned comment added by 70.29.47.136 ( talk) 15:05, 16 December 2009 (UTC)
Why is vascular headache an outdated term? The page implies that no headaches are now thought to be related to blood vessel swelling. This is at odds with the page for cluster headache which says "The intense pain is caused by the dilation of blood vessels". 81.131.54.224 ( talk) 16:08, 16 December 2009 (UTC)
does p-phenylenediamine degrade when exposed to air and/or light? if so how much? —Preceding unsigned comment added by 74.65.3.30 ( talk) 18:30, 16 December 2009 (UTC)
Hello,
I read and come to know that black holes do have charged and react to external charge, but how not known to me. Can you tell me please. —Preceding unsigned comment added by Harshagg ( talk • contribs) 19:03, 16 December 2009 (UTC)
Here is another question. We know that gravity is a weak force, compared to the electrostatic force. So it is conceivable that I have a black hole which is charged to a degree that the electrostatic repulsion is larger than the gravitational attraction. Does that mean that the black hole will start bleeding protons? In fact, does this mean that the even horizon is at different radii for negatively charged, positively charged, and neutral particle? The net force (sum of gravity and electrostatic) is certainly different for each... -- Stephan Schulz ( talk) 08:16, 17 December 2009 (UTC)
Do we 100% know where the continents were 300 million years ago or is this just a theory. Because The Future is Wild said Antartica was in the equator 300 million years ago, most show Artartica was in SP at that time. Is this right the further we go back in historical time, the less we know. Do we absolutely know if southern Africa was 75 degs. south 200 million years ago, some model shows southern Africa only 55 degs south at that time.-- 209.129.85.4 ( talk) 22:17, 16 December 2009 (UTC)
Please help me with these questions. I'm studying for finals and need to know the answers to these questions.
FILL IN THE BLANK
1. The velocity of an object moving in a straight line changes at a constant rate when the object is experiencing constant ____________?
2. The motion of an object looks different to observers in different ____________?
3. Speed is measured in units of _____________?
4. A moving object does not _______________ if its velocity remains constant?
5. The acceleration of a moving object is calculated by the deviding changes in _____________ by the time over which the change occurs.
6. Two or more velocities add by _____________?
7. The direction and length of a straight line from the starting point to the ending point of an object's motion is _______________?
8. Displacement and velocity are examples of _____________ because they have both magnitude and direction.
9. s=d/t is the equation that defines _______________?
10. The difference between speed and velocity is that velocity indicates the ______________ of motion and speed does not.
11. Because its _____________ is always changing, an object moving in a circular past experiences a constant change in velocity.
12. The SI unit for measuring _________________ is the meter.
13. Accelerated motion is represented by a(an) ___________________ line on a distance-time graph.
14. A constant slope on a distance-time graph indicates ____________ speed.
15. A cars speedometer measures _______________.
16. A car that increases its speed from 20 km/h to 100 km/h undergoes ________________ acceleration.
17. The sum of two or more vectors is called the ____________.
18. A distance-time graph indicates an object moves 20 km in 2 h. The average speed of the object is _____________ km/h.
SHORT ANSWER
19. In the equation for acceleration, a=v/t, how can you describe acceleration if the numerator is negative?
20. Vector addition allows you to add what two quantities for any number of vectors?
21. Distance is a measure of length. What information does displacement give in addition to distance?
22. What types of changes in motion cause acceleration.
23. What is the SI unit best suited for measuring the height of a building?
24. What information does the slope of a speed-time graph provide?
25. a=v/t is the equation for calculating the acceleration of an object. Write out the relationship shown in the equation using words.
26. Bus A travels 300 m in 12 s. Bus B travels 200 m in 12 s. Both vehicles travel at a constant speed. How do the distance-time graphs for these two speeds differ?
27. A child rolls a ball 4 m across a room. The ball hits the wall and rolls halfway back toward the child. Using vector addition, calculate the balls displacement.
28. How is motion described when the velocity of an object changes by the same amount each second?
29. What is the significance of the slope in a distance-time graph?
PROBLEM
32. If you ride your bike at an average speed of 2 km/hr and need to travel a total distance of 20 km, how long will it take you to reach your distance?
33. During a race, a runner runs at a speed of 6 m/s. Four seconds later, she is running at a speed of 10 m/s. What is the runner's acceleration?
34. Explain how velocity is different from speed?
35. Picture a ball traveling at a constant speed around the inside of a circular structure. Is the ball accelerating?
36. A girl walks from her home to a friend's home 3 blocks north. She then walks east 2 blocks to the post office, 1 block north to the library, and 1 block east to the park. From the park, she walks two blocks west to the movie theater. After the movie, she walks 4 blocks south to the pet store. What is the girls displacement from her starting point to the pet store? Where is the location of the pet store in relation to her home? Calculate the distance she walked in blocks.
MULTIPLE CHOICE
1. Instantaneous speed is measured
A) over a very tiny "instant" of time B) at the starting point C) when the object reaches its destination D) over the duration of the trip
2. The slope of a line on a distance-time graph is
A) displacement B) time C) speed D) distance
3. A person drives three blocks north, then turns east and drives 3 blocks. The driver then turns south and drives 3 blocks. How could the driver have made the distance shorter while maintaining the same displacement?
A) by driving north 1 block and east 4 blocks B) by driving back to the starting point by the same route C) by driving east 3 blocks by the starting point D) by driving west 3 blocks from the starting point
4. Which example identifies a change in motion that produces acceleration?
A) a ball moving at a constant speed around a circular track B) a particle moving in a vacuum at a constant velocity C) a vehicle moving down the street at a steady speed D) a speed skater moving at a constant speed on a straight track
5. A car traveling 88 km in 1 hour, 90 km in the next 2 hours, and then 76 km in 1 hour before reaching its destination. What was the car's average speed?
A) 209 km/h B) 63.5 km/h C) 74.5 km/h D) 254 km/h
6. Suppose you increase your walking speed from 1 m/s to 3 m/s in a period of 2 s. What is your acceleration?
A) 6 m/s squared B) 1 m/s squared C) 2 m/s squared D) 4 m/s squared
7. The slope of a speed-time graph indicates
A) acceleration B) direction C) speed D) velocity
8. Speed is the ratio of the distance of an object moves to
A) the motion of an object B) the direction the object moves C) the displacement of the object D) the amount of time needed to travel the distance
9. A ball is rolled uphill a distance of 3 meters before is slows, stops, and begins to roll back. The ball rolls downhill 6 meters before coming to a rest against a tree. What is the magnitude of the ball's displacement?
A) 9 meters B) 6 meters C) 18 meters D) 3 meters
10. The rate at which velocity changes is called
A) acceleration B) motion C) speed
D) vectorsPlease please please answer the ones you know(: please and thankyou! you will be of big help to do so. —Preceding unsigned comment added by Kaimorgan16 ( talk • contribs) 23:01, 16 December 2009 (UTC)
There is a very good Excel spreadsheet example of the Perceptron method in the article but the subtitles are incomplete and need additional entries which I plan to remedy shortly. Does anyone know where I can find a similar Excel spreadsheet example of an XOR capable layered ANN and one that displays all of the computations for Backpropogation? 71.100.0.206 ( talk) 23:17, 16 December 2009 (UTC)
Science desk | ||
---|---|---|
< December 15 | << Nov | December | Jan >> | December 17 > |
Welcome to the Wikipedia Science Reference Desk Archives |
---|
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages. |
How much time does it take for nuclear radiation from a bomb to decay to a safe level? —Preceding unsigned comment added by Cborgen ( talk • contribs) 00:05, 16 December 2009 (UTC)
From an article about a recently re-analyzed black hole - The outermost layers of the star are being siphoned by the black hole. The swirling gas forms a hot plasma disk around the black hole before it disappears, and the process emits a lot of X-rays and radio waves. The part in bold, can we observe that in motion? If Hubble takes a look at that pair and then looks back a day later - can we see a change? a week/month/year later? It's easy for me to visualize swirling masses of plasma being sucked off/out of a star and into the black hole, but I'm VERY curious about the timescales involved. Surely observation of the process-in-motion is possible with instruments, it being only a question of resolution? Are we there yet? Can we watch this happening or is it still the "snapshot" approach? 218.25.32.210 ( talk) 08:05, 16 December 2009 (UTC)
Hello. How is the main product of the condensation between propanoic acid and 3-aminopropanal named according to IUPAC nomenclature? I think that the aldehyde group in 3-aminopropanal does not react and naming the main product 3-formyl-N-propylpropanamide is ambiguous since the aldehyde group can be on the alkyl chain or the 'amide' chain by the naming alone. Is the main product a double-branched amine or a single-branched amide? Thanks in advance. -- Mayfare ( talk) 09:15, 16 December 2009 (UTC)
If you gathered all the insects in the world together, how much would they weigh in total? -- OpenToppedBus - Talk to the driver 11:47, 16 December 2009 (UTC)
why are atoms colourless, despite colour originally containing atoms has colour?
colour or paint is made from various compounds.Molecules combine to form compounds.a moleculeis formed by the combination of atoms.As we know that atom retains its identity throughout chemical change.therefore atoms should have colour —Preceding unsigned comment added by Omkar2510 ( talk • contribs) 12:54, 16 December 2009 (UTC)
See
HOMO-LUMO gap. The colour behaviour of a substance is determined by its chemical environment, e.g. electron charge density and the relative energies of various electronic orbitals.
John Riemann Soong (
talk)
18:57, 17 December 2009 (UTC)
In a combination of serial and parallel circuits, such as this one, am I correct to conclude that all three lamps shine equally brightly? My reasoning is that a and b/c are connected serially, so both a and b/c should get half of the voltage of the cell. B and c are connected in parallel, so they each get the full amount, thus all three each get half of the voltage of the cell. (I know this might sound like homework, but I am just trying to understand more about electricity and I have no teacher whom I can ask...) Lova Falk ( talk) 14:41, 16 December 2009 (UTC)
I have questions after reading http://news.bbc.co.uk/2/hi/science/nature/8414476.stm but don't know where to look in Wikipedia. (1) On a planet five time the mass of earth, what would the gravity be like? What would it be like to walk on the surface? (2) What are the odds of any given planetary atmosphere being breathable by humans? (3) How long would it take to travel to a planet 28 light years away using current technology? Thank you for helping. —Preceding unsigned comment added by 70.29.47.136 ( talk) 15:05, 16 December 2009 (UTC)
Why is vascular headache an outdated term? The page implies that no headaches are now thought to be related to blood vessel swelling. This is at odds with the page for cluster headache which says "The intense pain is caused by the dilation of blood vessels". 81.131.54.224 ( talk) 16:08, 16 December 2009 (UTC)
does p-phenylenediamine degrade when exposed to air and/or light? if so how much? —Preceding unsigned comment added by 74.65.3.30 ( talk) 18:30, 16 December 2009 (UTC)
Hello,
I read and come to know that black holes do have charged and react to external charge, but how not known to me. Can you tell me please. —Preceding unsigned comment added by Harshagg ( talk • contribs) 19:03, 16 December 2009 (UTC)
Here is another question. We know that gravity is a weak force, compared to the electrostatic force. So it is conceivable that I have a black hole which is charged to a degree that the electrostatic repulsion is larger than the gravitational attraction. Does that mean that the black hole will start bleeding protons? In fact, does this mean that the even horizon is at different radii for negatively charged, positively charged, and neutral particle? The net force (sum of gravity and electrostatic) is certainly different for each... -- Stephan Schulz ( talk) 08:16, 17 December 2009 (UTC)
Do we 100% know where the continents were 300 million years ago or is this just a theory. Because The Future is Wild said Antartica was in the equator 300 million years ago, most show Artartica was in SP at that time. Is this right the further we go back in historical time, the less we know. Do we absolutely know if southern Africa was 75 degs. south 200 million years ago, some model shows southern Africa only 55 degs south at that time.-- 209.129.85.4 ( talk) 22:17, 16 December 2009 (UTC)
Please help me with these questions. I'm studying for finals and need to know the answers to these questions.
FILL IN THE BLANK
1. The velocity of an object moving in a straight line changes at a constant rate when the object is experiencing constant ____________?
2. The motion of an object looks different to observers in different ____________?
3. Speed is measured in units of _____________?
4. A moving object does not _______________ if its velocity remains constant?
5. The acceleration of a moving object is calculated by the deviding changes in _____________ by the time over which the change occurs.
6. Two or more velocities add by _____________?
7. The direction and length of a straight line from the starting point to the ending point of an object's motion is _______________?
8. Displacement and velocity are examples of _____________ because they have both magnitude and direction.
9. s=d/t is the equation that defines _______________?
10. The difference between speed and velocity is that velocity indicates the ______________ of motion and speed does not.
11. Because its _____________ is always changing, an object moving in a circular past experiences a constant change in velocity.
12. The SI unit for measuring _________________ is the meter.
13. Accelerated motion is represented by a(an) ___________________ line on a distance-time graph.
14. A constant slope on a distance-time graph indicates ____________ speed.
15. A cars speedometer measures _______________.
16. A car that increases its speed from 20 km/h to 100 km/h undergoes ________________ acceleration.
17. The sum of two or more vectors is called the ____________.
18. A distance-time graph indicates an object moves 20 km in 2 h. The average speed of the object is _____________ km/h.
SHORT ANSWER
19. In the equation for acceleration, a=v/t, how can you describe acceleration if the numerator is negative?
20. Vector addition allows you to add what two quantities for any number of vectors?
21. Distance is a measure of length. What information does displacement give in addition to distance?
22. What types of changes in motion cause acceleration.
23. What is the SI unit best suited for measuring the height of a building?
24. What information does the slope of a speed-time graph provide?
25. a=v/t is the equation for calculating the acceleration of an object. Write out the relationship shown in the equation using words.
26. Bus A travels 300 m in 12 s. Bus B travels 200 m in 12 s. Both vehicles travel at a constant speed. How do the distance-time graphs for these two speeds differ?
27. A child rolls a ball 4 m across a room. The ball hits the wall and rolls halfway back toward the child. Using vector addition, calculate the balls displacement.
28. How is motion described when the velocity of an object changes by the same amount each second?
29. What is the significance of the slope in a distance-time graph?
PROBLEM
32. If you ride your bike at an average speed of 2 km/hr and need to travel a total distance of 20 km, how long will it take you to reach your distance?
33. During a race, a runner runs at a speed of 6 m/s. Four seconds later, she is running at a speed of 10 m/s. What is the runner's acceleration?
34. Explain how velocity is different from speed?
35. Picture a ball traveling at a constant speed around the inside of a circular structure. Is the ball accelerating?
36. A girl walks from her home to a friend's home 3 blocks north. She then walks east 2 blocks to the post office, 1 block north to the library, and 1 block east to the park. From the park, she walks two blocks west to the movie theater. After the movie, she walks 4 blocks south to the pet store. What is the girls displacement from her starting point to the pet store? Where is the location of the pet store in relation to her home? Calculate the distance she walked in blocks.
MULTIPLE CHOICE
1. Instantaneous speed is measured
A) over a very tiny "instant" of time B) at the starting point C) when the object reaches its destination D) over the duration of the trip
2. The slope of a line on a distance-time graph is
A) displacement B) time C) speed D) distance
3. A person drives three blocks north, then turns east and drives 3 blocks. The driver then turns south and drives 3 blocks. How could the driver have made the distance shorter while maintaining the same displacement?
A) by driving north 1 block and east 4 blocks B) by driving back to the starting point by the same route C) by driving east 3 blocks by the starting point D) by driving west 3 blocks from the starting point
4. Which example identifies a change in motion that produces acceleration?
A) a ball moving at a constant speed around a circular track B) a particle moving in a vacuum at a constant velocity C) a vehicle moving down the street at a steady speed D) a speed skater moving at a constant speed on a straight track
5. A car traveling 88 km in 1 hour, 90 km in the next 2 hours, and then 76 km in 1 hour before reaching its destination. What was the car's average speed?
A) 209 km/h B) 63.5 km/h C) 74.5 km/h D) 254 km/h
6. Suppose you increase your walking speed from 1 m/s to 3 m/s in a period of 2 s. What is your acceleration?
A) 6 m/s squared B) 1 m/s squared C) 2 m/s squared D) 4 m/s squared
7. The slope of a speed-time graph indicates
A) acceleration B) direction C) speed D) velocity
8. Speed is the ratio of the distance of an object moves to
A) the motion of an object B) the direction the object moves C) the displacement of the object D) the amount of time needed to travel the distance
9. A ball is rolled uphill a distance of 3 meters before is slows, stops, and begins to roll back. The ball rolls downhill 6 meters before coming to a rest against a tree. What is the magnitude of the ball's displacement?
A) 9 meters B) 6 meters C) 18 meters D) 3 meters
10. The rate at which velocity changes is called
A) acceleration B) motion C) speed
D) vectorsPlease please please answer the ones you know(: please and thankyou! you will be of big help to do so. —Preceding unsigned comment added by Kaimorgan16 ( talk • contribs) 23:01, 16 December 2009 (UTC)
There is a very good Excel spreadsheet example of the Perceptron method in the article but the subtitles are incomplete and need additional entries which I plan to remedy shortly. Does anyone know where I can find a similar Excel spreadsheet example of an XOR capable layered ANN and one that displays all of the computations for Backpropogation? 71.100.0.206 ( talk) 23:17, 16 December 2009 (UTC)