Are these solutions for waves correct?

[yeah:)]

Here is a link to an image of some questions on waves, with which I have been struggling, along with my attempts at each solution (in red):

http://www.flickr.com/photos/54527991@N06/5179422778/sizes/l/in/photostream/"

Please tell me if any of my solutions are wrong, and show me how I should have done them correctly. Also, please tell me what the specific term asked for in question 7 is. Thank you very much.

 

[Bhumble]

Prob 1, 3, 4, 5, 6, 8, 10, 12 Looks good.
Prob 2. f = 1/T. Take another look at this one.
Prob 7. I'm pretty sure they want you to know this is the period.
Prob 9. Looks like you made a mistake with this one.
Prob 11. Similar mistake as prob 9.

 

[yeah:)]

Thank you very much for that. The new solutions that I now have for questions 9 and 11 are 0.8 seconds and 0.25 seconds, respectively. Are those correct now?

As for question 2, I cannot see where I am not correct - could you please explain that one to me?

 

[collinsmark]

Thank you very much for that. The new solutions that I now have for questions 9 and 11 are 0.8 seconds and 0.25 seconds, respectively. Are those correct now?

[Edit: made a change about question 9.]
For question 9, your original answer was actually not correct, but neither is 0.8 seconds.

For question 11, the units of your answer needs to be in Hertz, not seconds.

As for question 2, I cannot see where I am not correct - could you please explain that one to me?

Your original answer for question 2 looks good to me as it is.

 

[Bhumble]

You are correct on prob 2. My mistake.

For prob 9 and 11
Period = T = 1/f
wave speed = f$$\lambda$$
=> T = $$\lambda$$/wave speed (units for period is in time usually seconds)

 

[yeah:)]

Thank you for that. The new answer I have for question 9 is 1/5 second (frequency=2.5/0.5=5 Period = 1/5 second.).

As for question 11, 60 waves/240 seconds = 0.25 Hz.

Are they correct now?

 

[collinsmark]

Are they correct now?

'Looks good to me.

 

[yeah:)]

Thank you very much!

 

[yeah:)]

Waves - Am I correct? (2)

Here is a link to an image of some questions on waves, with which I have been struggling, along with my attempts at each solution (in red):

http://www.flickr.com/photos/54527991@N06/5182568263/sizes/l/in/photostream/"

Please tell me if any of my solutions are wrong, and show me how I should have done them correctly.

 

[collinsmark]

Here is a link to an image of some questions on waves, with which I have been struggling, along with my attempts at each solution (in red):

http://www.flickr.com/photos/54527991@N06/5182568263/sizes/l/in/photostream/"

Please tell me if any of my solutions are wrong, and show me how I should have done them correctly.

1-7 and 9 look okay to me.

Something is wrong with 8. Probably just a silly mistake, but you should re-do it.

10 is also incorrect. You haven't evaluated the wavelength correctly.

 

[yeah:)]

Could you please point me in the direction of the mistake in 8?

Also, I cannot see where I am incorrect in 10 - is part c) not asking for a figure I used in part a)?

 

[collinsmark]

Could you please point me in the direction of the mistake in 8?

Redo your calculation of the frequency. Check your units and make sure your calculation is dimensionally correct.

Also, I cannot see where I am incorrect in 10 - is part c) not asking for a figure I used in part a)?

Part c) refers to the same figure as parts a) and b).

In your original solution you counted 4.0 waves on the 4.5 meter rope. Be a little more careful. The number of waves on the rope is not exactly 4.

 

[yeah:)]

8. Frequency = 5 Hz. x = 5 * 0.02 = 0.1m/s - correct?

10. I still do not quite understand this - are there only 3 waves there that should be counted? If it is not a round, whole number of waves, how should I go about counting them?

 

[collinsmark]

8. Frequency = 5 Hz. x = 5 * 0.02 = 0.1m/s - correct?

Looks okay to me.

10. I still do not quite understand this - are there only 3 waves there that should be counted? If it is not a round, whole number of waves, how should I go about counting them?

It's not a round, whole number of waves.

Start from the left. Take a look at what point in the wave shape the leftmost part of the rope is in (Hint: it's neither at a peak or a crest, but rather at the middle part of the rising half.) Then move to the right, and count up every time this point in the wave shape is passed again. What fraction of a wavelength is left over between your last count and the wall?

 

[yeah:)]

I see! There are 4.5 waves!

Therefore, a) x = 3 * 1 = 3 m/s b) time = 4.5/3 = 1.5 seconds c) 1 metre - correct?

 

[collinsmark]

I see! There are 4.5 waves!

Therefore, a) x = 3 * 1 = 3 m/s b) time = 4.5/3 = 1.5 seconds c) 1 metre - correct?

'Looks good!

 

[yeah:)]

Thank you very much for that!

 

[yeah:)]

Questions on Waves

Here is a link to an image of some questions on waves, with which I have been struggling, along with my attempts at each solution (in red):

http://www.flickr.com/photos/54527991@N06/5198496637/sizes/l/in/photostream/"

Please tell me if any of my solutions are wrong, and show me how I should have done them correctly. Thank you very much in advance for any help.

 

[Delphi51]

Check e iv. As you go from left to right through the diagrams, the wavelength decreases and it causes something else to happen to the diffracted waves. The shorter the wavelength, the less spreading into the shadow area.

f iii is a weak answer. The extra words in the question should lead you to a different answer, related to the one about less spreading with shorter wavelengths.

 

[kk727]

Everything looks good to me except your diagram that you drew in, and the very last question. The wording on (d) sounds fine to me, I wouldn't worry about that one. Just look back and see how wavelength affects diffraction for the diagram - which will also steer you towards the right answer for the last question. (the waves spread out less...think, accuracy of the tape measure)

 

[yeah:)]

Thank you for your comments. For e) iv), am I right in assuming that the waves should almost be completely straight?

As for the very last question, are you suggesting that ultrasonic waves are used because they are not diffracted as much as ordinary waves when they enter and leave the tape measure, hence increasing the accuracy of the overall measurement?

Also, is the reason that I have already provided for the very last question not a valid point to make (I understand that it is not the point the question was searching for, but is it valid?)?Were the rest of the answers completely correct?

 

[Delphi51]

Yes to all that!

 

[yeah:)]

Thank you very much for your help!

 

[Delphi51]

Most welcome! Good luck on the next one.

 

[yeah:)]

Questions on Waves

Here is a link to an image of some questions on waves, with which I have been struggling, along with my attempts at each solution (in red):

http://www.flickr.com/photos/54527991@N06/5199241951/sizes/l/in/photostream/"

Please tell me if any of my solutions are wrong, and show me how I should have done them correctly. Thank you very much in advance for any help.

 

[madmike159]

I would look at the a and b again, there not wrong, but the answers aren't wrong (I think) but there not detailed.
For c vi is it not to do with the device not being 100% efficient?
For e talk about standing waves if the food was not moving.