Physics - October 2007

Young David who slew Goliath experimented with slings before tackling the giant. He found that he could revolve a sling of length 0.600 m at the rate of 7.00 rev/s. If he increased the length to 0.900 m, he could revolve the sling only 5.00 times per second.
(a) What is the speed of the stone for each rate of rotation?
m/s at 7.00 rev/s, at m/s at 5.00 rev/s
(b) What is the centripetal acceleration of the stone at 7.00 rev/s?
(c) What is the centripetal acceleration at 5.00 rev/s?

2007-10-25 21:15:05 · 3 answers · asked by Justin 3

According to the universal law of gravitation, every object exerts a force on every other object in the universe. So if I move my hand, will the effect of that be felt in Alpha Centuari immediatly, or in 4 years time? If yes, would it be theoretically possible to devise meganisms for sending messages that move faster than light?

2007-10-25 19:33:21 · 7 answers · asked by kwaaikat 5

Two identical spheres of mass m and radius R are shot vertically with the same kinetic energy K . The first sphere is not spinning about its axis. The second sphere is spinning about its axis at angular frequency ω . What are the maximum heights of each sphere. The acceleration of gravity is g downward.

2007-10-25 17:14:04 · 6 answers · asked by Nik 1

This is part of a very long question involving graphs so I won't post the entire thing. I understand most of it, but the final part I couldn't get was finding the initial velocity of a projectile on another planet. I don't know the angle of the projectile. (The x's, o's, and y's are supposed to be subscripts.) I figured out that:
vx = 43.9m/s
projectile starts at 74m
max. height reached= 84.3m
t= 3.5s for the whole trip (until it hits the ground)
a= 24.6m/s^2

I tried using d=voyt + 1/2at^2 and I got voy= 67.14m/s, but when I plugged this in to the pythagorous equation vx^2 + voy^2 = vo^2, I ended up with 80m/s, which isn't correct.
The answer is around 48m/s (give or take a little) but I don't know how to arrive at this. Please help. Any suggestions would be great. Thanks!

2007-10-25 17:12:50 · 2 answers · asked by kanimikala 2

2007-10-25 15:53:00 · 2 answers · asked by Nicole 1

people need to know this stuff. http://www.youtube.com/watch?v=zORv8wwiadQ

2007-10-25 15:45:15 · 6 answers · asked by Pink Panther 4

2007-10-25 14:51:48 · 4 answers · asked by Anonymous

2007-10-25 14:49:11 · 5 answers · asked by Lisa L 1

also how do you find the Acceleration when they give you the Mass and Force?
What are the equations?

THANKS IN ADVANCE!

2007-10-25 14:40:08 · 5 answers · asked by Anonymous

Do these two categories cover ALL waves? As in, are all waves either electromagnetic waves and mechanical waves?

2007-10-25 14:22:02 · 6 answers · asked by Insert nickname here 2

2007-10-25 14:15:26 · 4 answers · asked by Anonymous

A factory worker accidentally releases a 210 kg crate that was being held at rest at the top of a ramp that is 4.1 m long and inclined at 30° to the horizontal. The coefficient of kinetic friction between the crate and the ramp, and between the crate and the horizontal factory floor, is 0.23. (a) How fast is the crate moving as it reaches the bottom of the ramp? (b) How far will it subsequently slide across the floor? (Assume that the crate's kinetic energy does not change as it moves from the ramp onto the floor.)

2007-10-25 13:49:06 · 1 answers · asked by Anonymous

Cobalt-60 is a radioactive isotope used to reat cancers of teh brain and other tissues. A gamma ray emitted by an atom of this isotope has an anergy of 1.33 MeV (million electron volts, 1 eV= 1.602x10^-19 J). What is the frequency in Hz and the wavelength (in m) of this gammy ray?

2007-10-25 13:40:15 · 1 answers · asked by xxiangel 2

2007-10-25 13:33:27 · 1 answers · asked by Sean R 1

The ramp is inclined at 34.0° with respect to the horizontal. The coefficient of kinetic friction between the log and the ramp is 0.810, and the log has an acceleration of 0.700 m/s2. Find the tension in the rope.

2007-10-25 13:23:17 · 1 answers · asked by Anonymous

Question 1:

A 440 g hoop 200 cm in diameter is rotating at 252 rpm about its central axis. What is its angular momentum?


Question 2:

A weightlifter's barbell consists of two 35-kg masses on the ends of a 20-kg rod 1.6 m long. The weightlifter holds the rod at its center and spins it at 7 rpm about an axis perpendicular to the rod.
What is the magnitude of the barbell's angular momentum?

Question 3:

Engineers redesign a car's wheels with the goal of decreasing each wheel's angular momentum by 23% for a given linear speed for the car. Other design considerations require that the wheel diameter go from 38 cm to 35 cm. If the old wheel had a rotational inertia of 0.42 kg·m2, what must be the new wheel's rotational inertia if the engineers are to achieve their goal?

2007-10-25 11:56:30 · 1 answers · asked by nathanr20 1

A flywheel of mass 188 kg has an effective radius of 0.63 m (assume the mass is concentrated along a circumference located at the effective radius of the flywheel).

(a) What torque is required to bring this wheel from rest to a speed of 122 rpm in a time interval of 29.8 s?

(b) How much work is done during the 29.8 s?

2007-10-25 11:31:29 · 1 answers · asked by jordo867 1

A fire hose held near the ground shoots water at a speed of 13m/s. At what angle(s) should the nozzle point in order that the water land 16 m away? Why are there two different angles?

2007-10-25 11:28:27 · 1 answers · asked by Anonymous

You have three cookies.

One of them contains and alpha emitter.
One of them contains a beta emitter.
One of them contains a gamma emitter.

You have to sit on one, throw one out the window, and eat the last one.

What would you do and why?

2007-10-25 11:27:46 · 4 answers · asked by Sal 5

(a) If the bob rises to a height of 0.137 m, what was the initial speed of the bullet?


(b) What was the speed of the bullet-bob combination immediately after the collision takes place?

2007-10-25 11:25:55 · 1 answers · asked by pcphil68 2

I always thought it depended on the mass of the object, but a friend disagrees......

2007-10-25 09:50:07 · 6 answers · asked by space0505 3

A brick (mass M) is fropped from height h onto a ball (mass m). The mass of M is much much greater than the mass of m. How high will the ball bounce after the collision in terms of h? The collision is perfectly elastic.


I would assume that if the collison is elastic, once the brick hits the ball, they would both bounce up together but that is only a guess. The answer is not 0. It is supposed to be some fraction of the original height. Thanks a lot for your help.

2007-10-25 09:33:38 · 1 answers · asked by Anonymous

does the angle of the two items after the collisions always equal 90??
see pic: http://img179.imageshack.us/img179/277/p...

what does this mean?:

"after the collision the two particles have velocities that are directed at equal angles of 46 degrees on either side of the original line of motion of the particle going vertically(x-direction) "

2007-10-25 09:27:47 · 2 answers · asked by alejxa 2

2007-10-25 08:40:20 · 1 answers · asked by Anonymous

A model rocket is fired vertically upward from rest. Its acceleration for the first three seconds is a(t) = 60t at which time the fuel is exhausted and it becomes a freely "falling" body. Fourteen seconds later, the rocket's parachute opens, and the (downward) velocity slows linearly to -18 ft/s in 5 s. The rocket then "floats" to the ground at that rate.

(a) At what time does the rocket reach its maximum height? (Give your answer correct to one decimal place.)
11.4 seconds.

(b) What is that height? (Give your answer correct to the nearest whole number.)
1409 ft.

(c) At what time does the rocket land? (Give your answer correct to one decimal place.)
I cannot find this for my life, if someone could show me the steps and the answer, it would be really appreciated. Oh, and the other two answers a and b have been verified correct.

2007-10-25 08:34:29 · 2 answers · asked by Ant 3

2007-10-25 08:21:05 · 1 answers · asked by hello 1

Book problems that im trying to figure out to do better on the test


1. Particle A is located at the origin, particle B at the point (x, y) = (25 cm, 0). What is the location of the center of mass?
xcm
ycm

2. If a particle of mass 4.8 kg is moving east at 10 m/s and a particle of mass 16 kg is moving west at 10 m/s, what is the velocity of the center of mass of the pair?

3. Two identical gliders on an air track are held together by a piece of string, compressing a spring between the gliders. While they are moving to the right at a common speed of 0.52 m/s, someone holds a match under the string and burns it, letting the spring force the gliders apart. One glider is then observed to be moving to the right at 1.30 m/s.
What velocity does the other glider have?
___ m/s to the left.

2007-10-25 08:16:54 · 2 answers · asked by Pr0ject 1

A truck with a mass of 4000kg is heading easy just before making a left turn on a flat, rough roadbed at a constant speed of 20 m/s. The radius of curvature of teh road is 100m

A- What is the direction and magnitude of the resultant force on the truck?

B- What is the monimum coefficient of static friction between the truck tires and the roadbed if the truck is not to slip?


HEEEEEELLLLLLLLLLLLLLLp!!!

2007-10-25 07:58:32 · 2 answers · asked by Anonymous

2007-10-25 07:25:50 · 5 answers · asked by Oki 1

A wire with a resistance of 8.33 x 10^– 5 ohm/cm carries a current of 1.28 amp.

(a) How many electrons move through the wire per second?
(b) What voltage is required to produce this current through 800-m wire?

2007-10-25 06:57:34 · 2 answers · asked by MiG 2