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  1. R

    Politician probablity help

    A committee of 50 politicians is to be chosen from among our 100 senators. If the selection is done at random, what is the probability that each state will be represented? My friend tried to help me out, and this is what he came up with. Since there are 2 senators from each state, you...
  2. R

    Easy physics problem, finding forumula

    I have included a picture. Question: What is the force on each wire if B = 1.656T, i = 10A, L1 = 7cm and L2 = 14cm? Now, I have checked my physics book, and the equation I have found is F_12 = mu_0*L*I1*I2/(2*pi*D) where D is the distance between the two wires, and L is the length of...
  3. R

    Infinite sheet of chargejust on sigma stuff

    I love it how people ask me these questions, and yet, I do not even know if I have the right answer. Ok, I have the net sigma charge for the 2nd slab, and I need to break it up into two individual parts, sigma_a and sigma_b, where 'a' is left side of slab2, and 'b' is right side of slab 2...
  4. R

    Infinite sheet of chargejust on sigma stuff

    An infinite nonconducting sheet of charge, oriented perpendicular to the x-axis, passes through x = 0. It has area density s1 = -3 µC/m2. A thick, infinite conducting slab, also oriented perpendicular to the x-axis, occupies the region between x = a and x = b, where a = 3 cm and b = 4 cm. The...
  5. R

    Electrostatic force problem help with vector parts

    Ok, I know what's up...just because its iscoceles triangle, it doesn't mean you have 70 degree angles. Just do inv tan of .14/.07 to get 63.4 degrees, and then the x-components will work out.
  6. R

    Expansion of ruler and rod help

    The length of a metal rod is measured to be 20.08 cm using a steel ruler when both the rod and the ruler are at 22oC. Both the rod and the ruler are raised to a temperature of 253oC. When the rod is measured at this higher temperature, its length is found to be 20.32 cm. **** a) What is the...
  7. R

    Simple thermo dynamics help

    A single 50g ice cube is dropped into a thermally insulated container holding 200g of water. The water is initially at 25oC and the ice is initially at -15oC. ********** a) What is the final temperature of the system after is has come to thermal equilibrium ? b) Now let's drop a second...
  8. R

    Torsion Pendulum

    A uniform meter stick is hung at its center from a thin wire. It is twisted and oscillates with a period of 5 s. The meter stick is then sawed off to a length of 0.76 m, rebalanced at its center, and set into oscillation. ****************** With what period does it now oscillate? Ok, I...
  9. R

    Dam problem

    Picture is included. You are working as a summer intern for the Illinois Department of Natural Resources (DNR) and are assigned to some initial work on water resources project. The department will be overseeing the construction of a dam to create a large fresh water lake that will be...
  10. R

    Energy of a Satellite

    A 1700 kg satellite is orbitting the Earth in a circular orbit with an altitude of 1800 km. a) How much energy does it take just to get it to this altitude? . . . Ok, I just need help getting the setup on this first part. The amount of energy need to get to this altitude would the...
  11. R

    Two asteroids

    Deep in space, two small asteroids wind up stationary, 1.7 km apart. Asteroid Fred has a mass of 14900 kg and Asteroid Betty has a mass of 16400 kg. *********** a) Assuming the zero of gravitational potential energy to be when the asteroids are in contact, what is the potential energy of the...
  12. R

    Gravitation, neutron starlooks simple

    Thank you so much man. I figured it out. Now I can rest easily.
  13. R

    Gravitation, neutron starlooks simple

    Sorry, you lost me for a second. Are you saying setup the gravitation attaction equation equal to the centripetal force equation? So (G*Me*m)/R^2=Me*v^2/R ?
  14. R

    Gravitation, neutron starlooks simple

    A neutron star is formed when a star has burned all its nuclear fuel and begins to collapse in upon itself. It then packs roughly the mass of our Sun into a region with the same radius as that of a small city while continuing to spin at very rapid rate. Let's say you have a neutron star with a...
  15. R

    Bowling ball help on small subpart

    Lol. Okay, I knew I had to use that equation, I should have said that earlier. I feel like I have all the pieces in front of me, but just putting it all together is the obstacle. One thing though, should I use one of those constant angular acceleration equations? Thats what I'm thinking I got...
  16. R

    Bowling ball help on small subpart

    I already knew that the speed of the ball surface with respect to the ground is zero. But I'm still clueless as to how to set up my calculations. Please excuse my questioning. I'm not a physics whiz like you doc al. :smile:
  17. R

    Bowling ball help on small subpart

    Um, the condition has something to do with friction? So the ball starts to roll when its greater than the force of friction against it?
  18. R

    Bowling ball help on small subpart

    picture is included. A bowling ball 28 cm in diameter is slid down an alley with which it has a coefficient of sliding friction of µ = 0.52. The ball has an initial velocity of 11 m/s and no rotation. g = 9.81 m/s2. Note: For a sphere Icm = (2/5)mr2. a) What is the initial deceleration of...
  19. R

    Pivoting Stickstuck on two smaller parts

    Lol, duh. I kept on thinking that sin 0 equaled 1. Man, I need some sleep. :p part d)Ok, the only forces working is gravity and the centripetal force. I know that centripetal force is F=m(v^2/r) and the force of gravity is going to be m*g I can get angular velocity by V=omega*r so...
  20. R

    Pivoting Stickstuck on two smaller parts

    Ok. The force of gravity is pointing downwards, thus r vector is also pointing downwards. Which means my theta is 0. Like Doc said, r is a vector from the pivot point to the point where the force is applied. So is the r zero in this case?
  21. R

    Pivoting Stickstuck on two smaller parts

    Ok. So yea, gravity is the only force in the vertical position. I am probably messing up the calculation of the net torque. I'm still new to this! So for net torque, is it going to be r*m*g*sin 90? or r*7.7kg*9.8m/sec^2*sin 90? but I'm not sure what my r is. It probably is really a...
  22. R

    Pivoting Stickstuck on two smaller parts

    A picture has been included for your viewing pleasure. A stick of uniform density with mass M = 7.7 kg and length L = 0.6 m is pivoted about an axle which is perpendicular to its length and located 0.16 m from one end. Ignore any friction between the stick and the axle...
  23. R

    Recoiling problem help

    recoiling problem help :( I've included a picture also. A circus cannon, which has a mass M = 4000 kg, is tilted at theta = 40°. When it shoots a projectile at v0 = 90 m/s with respect to the cannon, the cannon recoils along a horizontal track at vcannon = 1 m/s with respect to the ground...
  24. R

    Three pulling strings with tension

    Ok, I finally figured out the problem gnome. It was a lot of work, but thanks for the initial start.
  25. R

    Three pulling strings with tension

    Um, after a bit of work, I finally got these equations. T2x = T2*cos(130) T2y = T2*sin(130) T3x= T3*cos(-120) T3y= T3*sin(-120)
  26. R

    Three pulling strings with tension

    I've included a picture. Three strings, in the horizontal plane, meet in a knot and are pulled with three forces such that the knot is held stationary. The tension in string 1 is T1 = 3.6 N. The angle between strings 1 and 2 is 130° and the angle between strings 1 and 3 120° with string 3...
  27. R

    Two-Dimensional Kinematics: Ball on a string

    Zimm has his own way of doing things, but I think I may have found an easier way of going about it. By using this equation... y-y0=voy(t)+(1/2)g(t)^2 where y=0 yo=2.2m a=-9.8m/s/s Solve for t to get 0.6700 sec. Thats the time for the stone to hit the ground in the y direction. Now you...
  28. R

    Simple motion graphs i need some clarification

    Ok. Please look at the attachment for the first part, and this web link for the second part. [Broken] For the first worksheet, this is what I have so far. 1. A 2. D 3. F 4. E 5. B 6. C Is it...
  29. R

    Swimmer in river relative motion crap

    Big thanks! 1 more thing That was awesome. I figured out part b, thanks to you guys. Anyway, for part a) is there, perhaps, another way, maybe easier way of approaching the problem? I don't want to be stuck memorizing equations and stuff for the test.
  30. R

    Swimmer in river relative motion crap

    A river 570 ft wide flows with a speed of 6 ft/s with respect to the earth. A woman swims with a speed of 3 ft/s with respect to the water. a) If the woman heads directly across the river, how far downstream is she swept when she reaches the opposite bank? b) If she wants to be swept a...
  31. R

    How do you calculate mass yield of a solution?

    Mass yield: I believe this has to use some stoichiometry. So first write a balanced equation. Next figure out your initial numbers, and use the mole ratio to convert say from substance A to substance B. When you get the moles of substance B, you can then convert that into its molar mass...
  32. R

    Highway Patrol - Argh, looks so simple!

    Sup guys. I figured something out, HallsofIvy, you messed up on a tiny little part. :-) Since the car decelerated for 5 seconds, that meant it would have 10 seconds left cruising at a constant speed of 65mph. Thus, the last stretch of distance would be 65 mph (= 0.0180 miles per second) for...
  33. R

    One-Dimensional Kinematics: Height vs Time

    big thanks! Man, I would never have thought of that! Thank you so much.
  34. R

    One-Dimensional Kinematics: Height vs Time

    This problem has a picture. You can view it at Ok. Maybe I'm missing something here, but for part one, I thought free-fall acceleration would be 9.8 m/s^2. Of course, computer didn't take it, so is there a way to find it from the graph? As for...
  35. R

    Ball Thrown From Cliff

    A man on the edge of a cliff H = 42 m high throws a ball directly upward. It returns past him 2 s later. (H actually is the height of the point of release of the ball above the base of the cliff. Neglect air resistance.) (Hint - Gravity causes a downward acceleration at the rate g = 9.81 m/s2.)...
  36. R

    Accelerating object problem

    Here is the problem from one of my online homework site. :-( An object starts at time t = 0 with a velocity of v0 = +4 m/s and undergoes a constant acceleration of a = -17 m/s2. There's five small parts to this problem but I got 4/5 done. I'll post them anyway to give you guys a clearer...
  37. R

    Physics problem bugging me!

    thanks! Thank you so much. Thank God I found this forum today! :)
  38. R

    Physics problem bugging me!

    Ok, this is the problem. Grains of fine sand are approximately sphere of an average radius of of 50 ìm are made of silicon dioxide. A solid cube of this material with a volume of 1m3 has a mass of 2600kg. Question: What mass of sand grains would have a total surface area (the total area...