Physics - September 2006

I've read in a book that sounds are heard more clearly at nights and it was because of total internal reflection of waves going up.But I think the explanation is wrong because sound travels faster in denser medium than in rarerr medium.Please explain.

2006-09-24 08:44:01 · 12 answers · asked by pavan 1

if it was possible how long would it take from one point on earth to walk foward and reach the same point?

2006-09-24 08:43:27 · 3 answers · asked by Arroyo R 1

Your Professor is tired of having to use 9.8m/s^2 all the time to do his calculations concerning gravity. He wants to use a nice round number 10 m/s^2. How much mass would have to be added to the Earth to make this happen? What would the new radius of the Earth be? Assume that the density of the Earth will remain the same. Where could you get the mass needed?

2006-09-24 08:28:44 · 5 answers · asked by Shane W 1

Ok, here's the problem...

"The specific heat capacity of ice is about 0.5cal/g x degrees celsius. Supposing that it remains at that value all the way to absolute zero, calculate the number of calories it would take to change a 1-gram ice cube at absolute zero (-273 degrees celsius) to 1 gram of boiling water. How does this number of calories compare with the number of calories required to change the same gram of 100 degree celsius water to 100 degrees celsius steam?"

I've stared at this problem for a while, and I have no idea where to even start. Am i supposed to use the formula Q = mcDT? I have no idea! Please help!

2006-09-24 08:26:28 · 5 answers · asked by Anonymous

The 2 vectors 3i-7j (no k) and 2i+3j-2k define a plane (its the plane of the triangle with both tails at one vertex and each head at one of the other vertices).
Which of the following vectors is perpendicular to the plane?
a 4i+6j+13k
b -4i+6j+13k
c 4i-6j+13k
d 4i+6j-13k
e 4i+6j

I did the cross product and got
=i(AyBk-AkBy)+j(AkBx-AxBk)+k(A...
=14i+6j+23k

How do I go from here?

2006-09-24 08:15:50 · 3 answers · asked by dutchess 2

2006-09-24 07:48:07 · 6 answers · asked by bob l 1

An airplane is flying north at 500km/h. It makes a gradual 180degr. turn at constant speed, changing its direction of travel from north through east to south. The process takes 40s. The average acceleration of the plane for this turn in km/h.s is:
a 12.5 km/h.s, north
b 12.5 km/h.s, east
c 12.5 km/h.s, south
d 25 km/h.s, north
e 25 km/h.s, south


Ok, I know I have a=v^2/r and T=2pir/v to work with.
40 sec = 0.011 hr is half a revolution (180degr) and since T is a hole revolution I think T is 0.0222. Putting that into the equation, I get 1.768km for r.
I tried working the problem backwards by plugging in the answers but I just don't get it. (maybe I'm doing omething wrong with the units since a is normally m/s^2 and thesy give me the answer in km/h.s?)
Also the direction, I would say if you travel north and make a turn east and end up going south, the average direction is east, does that make sense?

2006-09-24 07:29:41 · 6 answers · asked by dutchess 2

If there were no air resistance, how long would it take a free-falling parachutist to fall from a plane at 3200 meters to an altitude of 350 meters, where she will pull her ripcord? What would her speed be at 350 m? (in reality the air resistance will restrict her speed to perhaps 150 km/hr.)

2006-09-24 07:19:00 · 3 answers · asked by micheal j 1

The equation for calculating the relativistic mass of a moving object is...

m = m0/ square root(1-(v^2/c^2))

where m is the relativistic mass of the object, m0 is the rest mass of the object, v is the velocity of the object, and c is the velocity of light.

Calculate the relativistic mass to rest mass ratio, m/m0, for an electron that has a velocity with respect to the observer that is 80.0% of the velocity of light.

2006-09-24 07:00:57 · 4 answers · asked by dreamz 4

Ok, here's the problem...

"Calculate the height from which a block of ice at 0degrees celsius must be dropped for it to completely melt upon impact. Assume that there is no air resistance and that all the energy goes into melting the ice (Hint: equate the joules of gravitational potential energy to the product of the mass of ice and its heat of fusion (335,000 J/kg)).

My problem is that I have no clue what formulas/equations to use for this. I realize that the equation for Potential Energy is PE = mgh. And the equation for Quantity of heat is Q = cmDT. But how would I apply them to this problem?

2006-09-24 06:55:31 · 3 answers · asked by Anonymous

There is a room in space floating out in no where. Inside this closed room is a tennis ball. The tennis ball is bouncing around the room at about 25 km/h. The room is 10 foot by 5 foot by 8 foot. Suddenly the universe is split into 1000 different universes. Each universe is exactly the same at the first moment. Now as soon as the universes start off on their own things start changing because of quantum uncertainty. The question is, to the human eye, how long would it take to notice differences in the velocity and position of the tennis balls. Will the difference be noticed in the first year? A thousand years? A million? Never? Immediatley?

And how long would it take to notice differences in a person who was in the same situation as the tennis ball? (IE: The brain)

I'm not expecting anyone to get this down very precise but I'd enjoy opinions/estimates. Thank you!

2006-09-24 06:55:07 · 4 answers · asked by Someone 2

a straight river with parallel banks flows at 4 km/h. A boat moves directly downstream relative to the water at 11 km/h. the velocity of the boat relative to the river bank is...?

2006-09-24 06:40:27 · 3 answers · asked by dreamz 4

I can't seem to figure out where the left most vector starts. I have drawn a diagram, you can view it by going to the following link

http://individual.utoronto.ca/asadzaman/problemdiagram.jpg

2006-09-24 06:40:09 · 1 answers · asked by Asad Z 1

2006-09-24 06:18:59 · 5 answers · asked by me 1

i need to figure out the wavelength of a 1.9GHz cellphone radiowave. so it would be 3x10^8 / 1.9 ghz to equal the wave length

2006-09-24 06:15:43 · 6 answers · asked by Diggler AKA The Cab Driver 1

2006-09-24 06:12:46 · 6 answers · asked by Kelly 1

2006-09-24 06:07:06 · 12 answers · asked by Anonymous

f(x) is a polynomial. f(-1) = 4. f(1) = -3. f(4) = -6. Then the graph of f(x) must cross the x-axis at least how many times?

Do I need to know the degree of the polynomial?

2006-09-24 06:04:19 · 5 answers · asked by Olivia 4

An object is dropped from rest and falls freely. After 6 seconds, Calculate the instantaneous speed, average speed and distance fallen?

2006-09-24 05:53:52 · 14 answers · asked by Hamza 1

12. Suppose you exert a horizontal push on a crate that rests on a level floor, and it doesn’t move. How much friction acts compared with your push?

13. As you increase your push, will friction on the crate increase also?

14. Once the crate is sliding, how hard do you push to keep it moving at constant velocity?

15. What is meant by free fall?

16. Why doesn’t a heavy object accelerate more than a light object when both are freely falling?

17. The ratio of circumference/diameter for all circles is pi. What is the ratio of force/mass for freely-falling bodies?

18. What two principal factors affect the force of air resistance on a falling object?

19. What is the acceleration of a falling object that has reached its terminal velocity?

20. If two objects of the same size fall through air at different speeds, which encounters the greater air resistance?

2006-09-24 05:50:50 · 4 answers · asked by Anonymous

lim ..... f(t) =
t=>0

2006-09-24 05:41:58 · 3 answers · asked by Olivia 4

Having a real hard time figuring out the position-time graph and the acceleration-time graph from the given velocity-time graph. Any hints,or suggestions, would be greatly appreciated.

2006-09-24 05:41:12 · 3 answers · asked by Kelly 1

2006-09-24 05:38:38 · 8 answers · asked by Anonymous

Why is it that, in cold winters, a tub of water placed in a farmer's canning cellar helps prevent canned food from freezing?

2006-09-24 05:37:40 · 2 answers · asked by Anonymous

2006-09-24 05:33:56 · 8 answers · asked by John F 1

Is there any instance in which a buoy weighs more than the displaced water and still floats? I'm willing to consider different shapes/materials/ or depths.

2006-09-24 05:29:49 · 2 answers · asked by NathanCoppedge 6

Why is it that, in cold winters, a tub of water placed in a farmer's canning cellar helps prevent canned food from freezing?

2006-09-24 05:12:55 · 1 answers · asked by MegN 1

3.)Two students are asked to find the height of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device , they take it to the roof of the bulding and drop it off, timing its fall. One student reports a fall time of 2.0 sec., and the other, 2.3 sec.. How much difference does the 0.3 sec make for the estimates of the building's height.

2006-09-24 05:07:34 · 2 answers · asked by micheal j 1

2.) A stone is dropped from the roof of a high building. A 2nd stone is dropped 1.50 seconds later. How far apart are the stones when the 2nd one has reached a speed of 12.0 meters/second.

2006-09-24 05:06:46 · 1 answers · asked by micheal j 1

1.) A 95-meter long train begins uniform acceleration from rest. The front of the train has a speed of 25 meter/second when it passes a railway worker who is standing 180 m from wherer the front of the train started. What will be the speed of the last car as it passes the worker.

2006-09-24 05:06:14 · 3 answers · asked by micheal j 1