Welcome to PHY 121 Blog Help. Here's how it works. For each homework question and lab report we will make a post, this will probably contain a few tips on what the problems are about and how to solve them. If you are stuck on something then instead of emailing us directly you should post a comment in reply to the relevant post. We will try to guide you through tough points and help you understand the problems and the concepts behind them.
Sunday, October 24, 2010
Ch9 3 #4
This a resonance question, and you are tapping at the resonance frequency. Why must this be the resonance frequency?
10 comments:
Anonymous
said...
I thought the only equation I had to use was T= 2pi* sqrt(m/k)
This is how I figured it out. My numbers were 1.6 g spider -> .0016 Kg = m, and every 3 seconds, so 3=T, in this case. I used the two equations, k= (mg/L) and T=(2pi)*sqrt(L/g).
Write it out, it's much easier.
Using T=(2pi)*sqrt(L/g), you can solve for L. Make sure to square EVERYTHING! Grandma's rule. That means, when you are squaring to get rid of the (L/g), you also square the 2pi and the T.
So I ended up having (9/(4pi^2))*9.81 to solve for L. Then, using that result, I plugged in for k=mg/L. So it ended up
k=(.0016*9.81)/(result from previous equation).
I really hoped I helped (and it doesn't end up wrong for you!) and didn't give everything away in the process! I just know how frustrating these questions can be.
^^BTW, I might have actually done this incorrectly...or the 'long way', but I got the correct answer. Other options I tried was m*(2pi/T)^2 = k, and reworking that again, I seemed to have given me the same answer, but that didn't happen the first time. Maybe I had a parenthesis error. However, the equation above may work better for you.
I have tried every way shown here on the help blog page and two different ways I found online. I keep coming back to the two same answers: .01 or 1.8*10^-4 .
My spider weighs 2.5g, I remembered to convert to kg, and my T was 3s.
The post shows the perfect way to do it. use the equation T=2pie*sqrt(L/g) so it turns into L=(T^2/4pie^2)*g and solve for a number. Then use k=mg/L and that's your answer. The first part, you get L=2.24. Then for k, you should get 0.0109 or 0.011. Try that.
all you have to do is use the equation T=2Pie Rad(m/k). The problem is that the system doesnt take the answer unless you give it precisely to 2 sig figs in your answer.
If your numbers are: every 3 seconds (T=3) and mass 1.2g (.0012kg) then u solve by doing this: 3= 2pie rad( .0012/k) After you do the algebra you get the answer as .005263789. For me , the system did not take the answer if i entered .005 , but once you enter .0053 (correct sig figs) it should take it.
10 comments:
I thought the only equation I had to use was
T= 2pi* sqrt(m/k)
but it doesn't work
That is the right equation. Make sure you remember to change g to kg.
my weight was 1.5g and tap every 3 seconds
i keep getting the same answer but it keeps sayings its wrong.
i get .059
This is how I figured it out. My numbers were 1.6 g spider -> .0016 Kg = m, and every 3 seconds, so 3=T, in this case. I used the two equations, k= (mg/L) and T=(2pi)*sqrt(L/g).
Write it out, it's much easier.
Using T=(2pi)*sqrt(L/g), you can solve for L. Make sure to square EVERYTHING! Grandma's rule. That means, when you are squaring to get rid of the (L/g), you also square the 2pi and the T.
So I ended up having (9/(4pi^2))*9.81 to solve for L. Then, using that result, I plugged in for k=mg/L. So it ended up
k=(.0016*9.81)/(result from previous equation).
I really hoped I helped (and it doesn't end up wrong for you!) and didn't give everything away in the process! I just know how frustrating these questions can be.
^^BTW, I might have actually done this incorrectly...or the 'long way', but I got the correct answer. Other options I tried was m*(2pi/T)^2 = k, and reworking that again, I seemed to have given me the same answer, but that didn't happen the first time. Maybe I had a parenthesis error. However, the equation above may work better for you.
I have tried every way shown here on the help blog page and two different ways I found online. I keep coming back to the two same answers: .01 or 1.8*10^-4 .
My spider weighs 2.5g, I remembered to convert to kg, and my T was 3s.
What on earth am I doing wrong???
The post shows the perfect way to do it. use the equation T=2pie*sqrt(L/g) so it turns into L=(T^2/4pie^2)*g and solve for a number. Then use k=mg/L and that's your answer.
The first part, you get L=2.24. Then for k, you should get 0.0109 or 0.011. Try that.
Help me with part G of the first one please??
got part G, never mind. Hope my post helped though!
all you have to do is use the equation T=2Pie Rad(m/k). The problem is that the system doesnt take the answer unless you give it precisely to 2 sig figs in your answer.
If your numbers are: every 3 seconds (T=3) and mass 1.2g (.0012kg) then u solve by doing this: 3= 2pie rad( .0012/k)
After you do the algebra you get the answer as .005263789. For me , the system did not take the answer if i entered .005 , but once you enter .0053 (correct sig figs) it should take it.
Post a Comment