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anony12 · May 28, 2009, 04:38 PM

Q. A cylinder is measured and found to be 27 m long and 34 m in diameter.

1. What is the radius of the cylinder?
Would the answer just be 34/2=17

2. What is the volume of the cylinder in m3?
I got an answer of 2.45*10^4

Are my answers right?
Thank you

Perito · May 28, 2009, 07:58 PM

1. Correct.
2. Correct.

anony12 · May 29, 2009, 12:09 AM

Ok. Thanks a lot for that.

I have another q. that I want to make sure is right, thanks

Q. One mile is equivalent to 1609 m so 56 miles per hour is what speed in metres per second?

I got an answer of 25 m/s. I hope I'm right.

Perito · May 29, 2009, 01:49 AM

Q. One mile is equivalent to 1609 m so 56 miles per hour is what speed in metres per second?

I got an answer of 25 m/s. I hope I'm right.

You are correct.

I'm going to show you a simple way to do this. This is called (by some), "dimensional analysis". Note how the miles cancel, the hours cancel, and you're left with meters/sec.

$\frac {56\,mile}{1\, hour} \times \frac {1609\,m}{1\,mile} \times \frac {1\, hour}{3600 \,sec} = \frac {25\,m}{sec}$

If you didn't know that there were 3600 sec/hour (1 hour/3600 sec), you could do it this way:

$\frac {56\,mile}{1\, hour} \times \frac {1609.3\,m}{1\,mile} \times \frac {1\, hour}{60 \,min} \times \frac {1\,min}{60\,sec} = \frac {25\,m}{sec}$

In this case, mile cancels, hour cancel, min cancel, and you're left with m/sec. This is nice because you only have to remember a few conversions -- you can generate the others. Of course, there's always Google calculator:

Google: convert 56 miles per hour to meters per second

anony12 · May 29, 2009, 08:18 PM

yes. This is the approach I did to answer the question.

I have another similar question.

Q. Convert 13.6 g/cm3 to kg/m3.

1000g=1kg
(100cm)^3=(1m)^3

13.6g/cm^3 * 1kg/1000g * 10^6cm^3/1m^3
= 13600kg/m^3

could you please check if I'm right.
thanks

Perito · May 30, 2009, 05:18 AM

Convert 13.6 g/cm3 to kg/m3.

13.6g/cm^3 * 1kg/1000g * 10^6cm^3/1m^3 = 13600kg/m^3

Correct. $13.6 \,\frac {g}{cm^3} = 13600\,\frac {kg}{m^3}$

anony12 · Jun 2, 2009, 09:22 PM

Can someone please look over my answer to this question please.

Q. What multiple of its initial intensity I0 does the intensity of an electromagnetic wave change to if the amplitude of its electric field increases from E0 to 3E0 ?

I believe the answer is 9 as we go 3^2. Am I right?

anony12 · Jun 3, 2009, 09:23 PM

I need someone's help please for the above question.

Perito · Jun 4, 2009, 07:27 AM

I think your answer is right, but I need to look up the formulas involved to be sure.