Understanding Snapshot and History Graphs for Waves

[bcjochim07]

Homework Statement

figure is asnapshot.jpg

correct & incorrect graphs is aasnapshot.jpg

Draw the history graph D(x=0m, t) at x= 0m for the wave shown in the figure.

Homework Equations

The Attempt at a Solution

I'm not quite understanding the concept of snapshot and history graphs. I think for this one the problem is that is is moving left. The graph that I drew is the wrong one. Here was my reasoning: In the figure, the graph is moving left, so shouldn't the leftmost point on the wave hit the point first? If at t=2 s this leftmost point is 1m away from x=0, then it takes 1 sec for it to arrive, so at t=3. I don't think I am visualizing this at all correctly. Could someone please explain to me why the graph on the bottom is correct? Thanks!

 

[bcjochim07]

Any thoughts would be greatly appreciated.

 

[bcjochim07]

I am confused and this is really bothering me.

 

[Redbelly98]

The Attempt at a Solution

I'm not quite understanding the concept of snapshot and history graphs. I think for this one the problem is that is is moving left. The graph that I drew is the wrong one. Here was my reasoning: In the figure, the graph is moving left, so shouldn't the leftmost point on the wave hit the point first?

Yes.

If at t=2 s this leftmost point is 1m away from x=0, then it takes 1 sec for it to arrive, so at t=3.

Yes, nothing happens (at x=0 m) until t = 3 sec.

I don't think I am visualizing this at all correctly. Could someone please explain to me why the graph on the bottom is correct? Thanks!

It's not correct. At x = 0, D is 0 until t=3 sec. The graph labeled "wrong" looks like the right one to me.

 

[bcjochim07]

Yeah, see I'm having problems because there are a couple problems like this in my textbook where my drawings are completely off from what the back of the book has, so I was worried that I was not understanding this at all.

 

[Redbelly98]

Wow. What's the name of this book, and the authors? Looks like you understand it better than they do!

 

[freshfruit007]

My answer is the same as the original poster's..please, what are we doing wrong?!??!

 

[Redbelly98]

Welcome to Physics Forums

You and the OP did it right, the book has it wrong.

What is the name of this book and its author?

 

[Klorey]

The book's called Physics for Scientists and Engineers: A Strategic Approach (2nd ed.), Vol 3, and the author is Randall D. Knight. I also got the same answer as the OP. So the book is wrong and the OP is right?

 

[Redbelly98]

Welcome to PF

The book's called Physics for Scientists and Engineers: A Strategic Approach (2nd ed.), Vol 3, and the author is Randall D. Knight. I also got the same answer as the OP. So the book is wrong and the OP is right?

You are correct.

And thank you for answering my question

 

[Klorey]

No problem Thanks for the help (and the fast reply)!

 

[Epsillon]

I have the 6th edition of this book and the answer in the answer key is still wrong...