Physics - March 2007

I am still not understanding it: Here is the question

Find the ' y ' component of the center of mass for a uniform solid cone of radius ' R ' and height ' h '. The answer should be expressed as a (numeric) fraction of ' h ', measured from the base of the cone.

I found an example that worked out how to find the center of mass of a square pyramid.

The way they worked it out as follows, they said that the mass of a slab of thickness dy at a height y is

dm = p(Density) * dV.

Then they said the Y coordinate of center of mass is
Ycm = 1 / M * S(Integral) y dm

They then said that the total mass is

M = S(Integral) dm = S(Integral) slab thickness dy

They then got Ycm = S(Integral) y^3 dy / S(Integral) y^2 dy

They then took that expression and integrated from 0 to h, and expressed Ycm as a fraction of h. I don't really understand this and how to apply it to a cone. A thorough step by step explanation in words along with the mathmatical expressions will really help.

2007-03-25 18:00:08 · 5 answers · asked by Anonymous

2007-03-25 17:59:47 · 10 answers · asked by ammi 1

2007-03-25 17:20:25 · 11 answers · asked by Anonymous

the hill is 30m high and 100m long and makes an angle of 40degrees with the horizontal. The coefficient friction between the tires of the bicycycle and the hill is .30. what is the work done by friction on the girl and her bicycle at the bottom of the hill. I think the answer is -9009J. I know W=f*d cos theta but im just having trouble (especially drawing the picture)

2007-03-25 17:15:35 · 1 answers · asked by Greg 1

2007-03-25 17:10:18 · 3 answers · asked by Anonymous

A charged rod is brough near a pile of tiny spheres. Some of the spheres are attracted to the rod, but as soon as they touch the rod, they fly away in different directions. Explain why.

2007-03-25 17:01:47 · 2 answers · asked by Ha!! 2

2007-03-25 16:50:09 · 1 answers · asked by bhelreden 1

Hello, I am a software professional from 8+ years but have retained some passion for physics and mathematics. I read some books on modern physics as time permits, but the idea of not being able to spend enough time and not being able to understand mathematically bugs me.

1. Can any one suggest what is the best way to ramp up and be able to appreciate latest papers ?
2. Are there any published study plans / groups that you are aware of ?
3. Do you think self study can take me anywhere near reaching my goal ?

2007-03-25 16:45:30 · 2 answers · asked by Raj 1

alex throws a .15kg ball down onto the floor. the ball's speed just before impact is 6.5m/s, and just after is 3.5m/s. if the ball is in contact with the floor for .025s, what is the magnitude of the average force applied by the floor on the ball?

how do i figure this out??

2007-03-25 16:38:54 · 3 answers · asked by Anonymous

How do I solve this??

2007-03-25 16:31:11 · 1 answers · asked by Anonymous

I am required to make a contraption for my physics class that will prevent a large, grade A egg from breaking when dropped from one meter, three meters and one story.

Its dimesions cannot exceed 6 inches and it can only be made of toothpicks and adhesive.

I can make a parachute out of toothpicks and glue and that is not included in the 6 inches.

Please help this is due in like 3 days.

2007-03-25 16:22:14 · 7 answers · asked by DeSmetWaterPolo4 2

Everything you know about who made the ecuation or proved it experimentaly will be helpful, thanks

2007-03-25 16:17:24 · 2 answers · asked by ealr1980 2

1. A boy left camp and rode his bicycle due north for 45 m. He then turned and road due east to a bridge over a river where the bearing to the campsite was 210°. He then continued to a railway station where the bearing to the campsite was 246°. Calculate:
a) the distance to the camp from the bridge
b) the distance to the camp from the railway station
c) the distance from the bridge to the station

My answers:
a) distance=52m
b) distance=110.6m(to 1.decimal place)
c) distance=75m (to 1.decimal place)

2. In the triangle PQR, find the size of angel Q given that angle QPR
measures 59°, QR is 19.5km and PR is 14.8km.

My answer: angle Q=40.5° (correct to 1. decimal place)

Are my answers correct? Please tell me if they are incorrect. I have gone over these but I can't work out if anything is wrong with them.
I live in Australia...these conversions might help...
1cm(centimetre)=0.01m(metre)
10cm=0.1m
100cm=1m

1000m=1km(kilometre)

2007-03-25 16:11:05 · 1 answers · asked by Anonymous

Question: The length of two sides of a triangle are 9.3cm and 10.5cm and the included angle is 71°. Calculate:
a) the area of the triangle
b) the perimeter of the triangle

My answer:
a) Area=46.2cm^2
b) Perimeter=33.5cm (correct to 1.decimal.place)

2. A surveying team marks off two positions P and Q. They are on level ground, on the same side of a hill and in line with the hill. The horizontal distance from P to Q is 1200m and the team measure the angle of elevation of the summit of a hill from P and Q as 21° and 71° respectively. Find the height of the hill.

My answer: Height of hill=822.1m (correct to 1. decimal place).

Are the answers for question 1. a and b and question 2 correct? I have spent many hours on all of these questions. Could you please tell me if they are wrong?

Also I live in Australia...if you are not familiar with centrimetres(cm) and metres (m) here are a few conversions:
1cm=0.01metre
10cm=0.1metre (m)
100cm=1metre

1000metres=1kilometre (km

2007-03-25 16:09:25 · 4 answers · asked by Anonymous

What I mean is that being an undergraduate student, beyond my thesis research, if I started some other kind of research, and I'm yet not a part of an university, is there some way I could get my research paid?, after publishing it on Arxiv.org for example.? Or does it depend more on my university and my country?; does someone know the case for Mexico and its CONACYT (National Science and Technology Counsil)?, Can someone live of pure research without being a part of an university?, I appreciate a lot each of your answers, thank you.

2007-03-25 15:55:05 · 2 answers · asked by LGNR 3

In shape and wavelength

2007-03-25 15:39:44 · 1 answers · asked by Erosh 2

2007-03-25 15:26:42 · 6 answers · asked by sky_blue 1

a solid brass ball of mass m and radius r will roll without slipping along the loop-the-loop track when released from rest along the straight section. For the following answers use g for the acceleration due to gravity, and m, r, and R, as appropriate, where all quantities are in SI units.



(a) From what minimum height h above the bottom of the track must the marble be released to ensure that it does not leave the track at the top of the loop? (The radius of the loop-the-loop is R. Assume R r.)

(b) If the marble is released from height 6R above the bottom of the track, what is the magnitude of the horizontal component of the force acting on it at point Q?

2007-03-25 14:28:08 · 1 answers · asked by x2carlosp 2

a solid cylinder of radius 7 cm and mass 16 kg starts from rest and rolls without slipping a distance L = 6.0 m down a roof that is inclined at angle = 30°.

Scenario: The cylinder slides down a roof for a distance L, the roof is inclined at a 30 degree angle with the horizontal, and the roof is a height H above the ground.

(a) What is the angular speed of the cylinder about its center as it leaves the roof?
rad/s
(b) The roof's edge is at height H = 5.0 m. How far horizontally from the roof's edge does the cylinder hit the level ground?
m

2007-03-25 14:26:22 · 1 answers · asked by x2carlosp 2

Here is the question:

Find the ' y ' component of the center of mass for a uniform solid cone of radius ' R ' and height ' h '. The answer should be expressed as a (numeric) fraction of ' h ', measured from the base of the cone.

If someone could show me a step by step process on how to conquer this problem, it would really help.

2007-03-25 14:21:16 · 1 answers · asked by Anonymous

An automobile traveling at 50.0 km/h has tires of 80.0 cm diameter.


(a) What is the angular speed of the tires about their axles?
rad/s

(b) If the car is brought to a stop uniformly in 25.0 complete turns of the tires (without skidding), what is the magnitude of the angular acceleration of the wheels?
rad/s2

(c) How far does the car move during the braking?
m

2007-03-25 14:21:03 · 1 answers · asked by x2carlosp 2

The area under the Force versus Distance represents:

a force.

b momentum.

c power.

d work.

2007-03-25 14:16:22 · 2 answers · asked by mac_addict 3

A one-piece cylinder is shaped as in the figure below, with a core section protruding from the larger drum. The cylinder is free to rotate around the central axis shown in the drawing.
A rope wrapped around the drum, of radius 1.38 m, exerts a force F1 to the right on the cylinder. A rope wrapped around the core, of radius 0.465 m, exerts a force F2 downward
on the cylinder.
Let F1 = 4.42 N and F2 = 7.37 N.

What is the net torque acting on the cylinder about the rotation axis (which is the z axis in the figure)? Answer in units of Nm

2007-03-25 14:04:00 · 2 answers · asked by mansun15 1

Sci HW

2007-03-25 13:59:21 · 1 answers · asked by jl171994 1

I've been doing a lot of reading on the subject of Quantum Mechanics lately. I'm in no way a physicist but this subject greatly interests me. But with that said, let me just jump into my question.

Let's say a civilization in the FAR future came up with a way to manipulate the probability wave of, say, an electron. I know they would have to do this without the observer in the equation and all that, so I won't begin to speculate how it will be possible. So let's just say they could manipulate this probability wave.

What's going to happen to that electron if they make the wave "read" zero at every possible point, making it so the electron has no probability to exist anywhere in the universe? Now what's going to happen if they "add a probability" to the wave that was "reading" zero?

I know these are probably pointless questions, I'm just curious as to what everyone else thinks might happen in these situations.

2007-03-25 13:53:12 · 4 answers · asked by Anonymous

A sinusoidal EM wave has an electric field amplitude Em = 39.0 mV/m. What are the intensity and average energy density? [Hint: Recall the relationship between amplitude and rms value for a quantity that varies sinusoidally.]

average energy density?
intensity?

2007-03-25 13:36:07 · 1 answers · asked by David S 2

2007-03-25 13:31:58 · 1 answers · asked by M3 3

A 30.0 W laser emits a beam of light 6.0 mm in diameter. The laser is aimed at the Moon. By the time it reaches the Moon, the beam has spread out to a diameter of 85 km. Ignore absorption by the atmosphere.

What is the intensity of the light just outside the laser?

What is the intensity of the light where it hits the surface of the Moon?

2007-03-25 13:26:32 · 1 answers · asked by David S 2

2007-03-25 13:04:31 · 2 answers · asked by sbconfused 1

Must include the terms air resistance, gravity, and terminal velocity.

2007-03-25 12:57:58 · 3 answers · asked by Jen25 2