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  1. O

    Static frictions and moving boxes on top of a box

    Homework Statement http://www.screencast.com/users/trinhn812/folders/Jing/media/d77fab7d-ece6-4c9c-be65-bf41f94770fd Homework Equations I got the right answers doing the work shown, but I don't understand the logic of how I solved question 4. The Attempt at a Solution
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    Calculate wavelength of electron

    Homework Statement http://www.screencast.com/users/trinhn812/folders/Jing/media/9582a1aa-b21a-4e50-8774-b60866a7d666 Homework Equations lambda=h/p The Attempt at a Solution So I got 4.04E-12 m but the book says the answer is 3.23pm I'm not sure where I'm wrong
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    How far from the lightbulb can you stand to see it? photon problem

    Homework Statement http://www.screencast.com/users/trinhn812/folders/Jing/media/23298f1b-2ef4-4cdf-8b7a-58c9be07335a Homework Equations E=hf The Attempt at a Solution I'm not even sure how to get the distance for this problem.
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    Conservation of energy and electrons in electric field?

    Homework Statement http://www.screencast.com/users/trinhn812/folders/Jing/media/6596c399-feb6-49cf-82a7-d6d16c2a88e8 Question 17 Homework Equations So I solved this problem using kinematics and would like to learn how to solve it use conservation of energy. I can't seem to get the right...
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    Monochromatic light and reflection

    http://www.screencast.com/users/trinhn812/folders/Jing/media/07c73e88-45a9-4703-91e1-237b20135d2c I'm not sure why the answer is A. I tried reasoning myself that it has to do with the critical angle, but I can't seem to convince myself.
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    Plagued by Snell's law and geometry

    I'm just having a horrendous time trying to figure this problem out. My geometry is really lacking. http://www.screencast.com/users/trinhn812/folders/Jing/media/64c9342a-985a-4bb2-9e29- [Broken] 98b5b5ebb1ad
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    Thin hair diffraction

    So I understand that thin hair or wire can make a diffraction pattern, but why would the diffraction pattern be horizontal when the hair is vertical?
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    LRC circuit:what is the voltage of the capacitor when the generator is at maximum vol

    Homework Statement http://www.screencast.com/users/trinhn812/folders/Jing/media/cdd8b2f4-1c0d-43ba-8722-fb8b811c5585 Homework Equations V=IR V(C)=X(C)*R The Attempt at a Solution I'm having trouble with number two. I tried finding Z from the frequency and then calculating the...
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    In what direction does the sphere move between two positive charges

    Homework Statement http://www.screencast.com/users/trinhn812/folders/Jing/media/8fe997e1-46e5-4033-a246-fbad0acb7162 Homework Equations The Attempt at a Solution I understand that in question 25, the conductor becomes polarized and its negative charges will be more attracted...
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    Korkhoff's loop rule

    http://www.screencast.com/users/trinhn812/folders/Jing/media/3bedaa97-7020-4c5b-85d8-213de24b30a5 For the above problem. A helpful yahoo user told me that I can prove the answer for the above question by solving the problem. He said: Total current is 9/6.2 = 1.45 amps. that all flows thru the...
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    RC circuit and kirchoff's loop rule

    http://www.screencast.com/users/trinhn812/folders/Jing/media/de5edaba-e848-47f5-82b9-bd770b216e95 I need help with Question 27 specifically. The correct answer is A, but I don't understand why. I thought it would be B according to Korkoff's Loop rule of the inner left loop, where current...
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    Why would voltage stay the same when a dielectric is introduced?

    http://www.screencast.com/users/trinhn812/folders/Jing/media/9527c4fa-05b4-4baa-98ee-2a3ad47e7e5a I need an explanation for question 6. Why would voltage stay the same across capacitor 3? The dielectric increases capacitance which is inversely related to voltage correct? The equation...
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    Center of mass: What would make the truck tipover?

    Homework Statement http://screencast.com/t/ZTk3NDUxNjU I need help with understanding number 18. Homework Equations Center of mase formula: m1x1+m2x2/(all masses) The Attempt at a Solution How do you tell if adding the weight will make the truck tipover. I calculated that...
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    Multi Tube and fluid pressure

    Homework Statement Now two fluids are placed in the same tube (d). Both sides are open to the atmosphere without pistons. One fluid is water and the other (on top of the water in the left branch of the tube) is an oil of unknown density. l = 135mm and d = 12.3mm. What is the density of the...
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    How to calculate impulse when velocity is angled?

    Homework Statement Compare impulse for the two objects http://www.screencast.com/users/trinhn812/folders/Jing/media/ecf05e80-8fa7-435c-bfa0-891cf13b176a Homework Equations Change in impulse equation The Attempt at a Solution When you calculate impulse do you have to find the...
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    Conservation of energy in elastic collision

    Homework Statement http://www.screencast.com/users/ntrinh3/folders/Jing/media/a4165a56-de0d-4a4a-a01e-49242fd505c4 Need help with question 13 Homework Equations Conservation of energy and momentum occurs in elastic collision The Attempt at a Solution Why would the block 2 have an...
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    How do you calculate Center of mass

    Homework Statement I'm confused about how to find the center of mass http://www.screencast.com/users/ntrinh3/folders/Jing/media/a9773d23-38f1-4d28-a6f8-3b681d42d4c2 and http://www.screencast.com/users/ntrinh3/folders/Jing/media/bfb40c40-0068-41e8-ac83-2146e1df3330 Homework...
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    Calculating velocity of a block on a slope using work theorem

    Homework Statement http://www.screencast.com/users/ntrinh3/folders/Jing/media/7b6a2810-2827-44c3-adfc-cd27d564b812 Homework Equations Wnet=change in KE The Attempt at a Solution so I made the coordinate with x positive in right direction and y is positive up. Fdcos30-mgh=.5mv^2...
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    Which forces does work as a car brakes?

    Homework Statement Which forces does work? http://www.screencast.com/users/ntrinh3/folders/Jing/media/3f09a85d-142c-4f73-a8a8-1ad506d5c2b8 Homework Equations W=fdcos(theta) The Attempt at a Solution I always thought normal and friction does no work because it is perpendicular to...
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    Calculate the energy lost to friction

    1. Homework Statement http://i43.tinypic.com/i1bq1i.jpg I need help with number 9 2. Homework Equations Wnet=change in KE Wnc=Change in Energy The Attempt at a Solution so I'm assuming the energy dissipated means the work done by friction? so work of friction is umgcos(15)*d...
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    Calculation loss of energy due to friction?

    Homework Statement http://i43.tinypic.com/i1bq1i.jpg I need help with number 9 Homework Equations Wnet=change in KE Wnc=Change in Energy The Attempt at a Solution I haven't been able to get the answer marked by the computer. I tried Fs(h*cos15)=.5mv^2-mgh and that is way off...
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    2 Block and a pulley(has mass) system

    Homework Statement http://i43.tinypic.com/352nlw2.jpg I need help with the question 25. The three star (hardest) problem. Homework Equations well conservation of energy is Mgh=.5Mv^2+.5Mv^2+.5(.5MR^2) ω^2 The Attempt at a Solution Wouldn't increasing the Radius increase the...
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    Phsyics Kinematics: cannonball shot straight up

    http://www.screencast.com/users/trinhn812/folders/Jing/media/5c3b51ea-aed8-4321-964c-126b49a3c1dc F/m = 0.3m/s^2 distance in x direction= 1/2(a)(T^2) By placing v(y) =0 and v(initial)=100 I found the time to be 20 sec. But my answer is 60m. So 1020-60=960m Wouldn't the ball misss the...
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    Would KE be more if a ball was thrown at a smaller angle?

    http://www.screencast.com/users/trinhn812/folders/Jing/media/bf95a29f-4bb7-4f18-8d2b-f0b90dc3af51 I'm not sure how KE would increase when the initial speed is still the same.
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    Calculating centripetal acceleration between moon and satelite

    Homework Statement http://www.screencast.com/users/trinhn812/folders/Jing/media/e79a7b88-f71e-4790-a35c-7bc0c3e03ec8 Answer key is marked Homework Equations F=gMm/r^2 =ma=mv^2/R The Attempt at a Solution So does gMm/r^2 also measure centripetal acceleration?
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    Physic:Calculating mass of one rail car?

    Physic:Calculating mass of one rail car? http://www.screencast.com/users/trinhn812/folders/Jing/media/0852e68e-acef-49b1-a54d-39289386b978 I'm confused. Why isn't it 10000N/10car=1000N*1m/s^2=1000kg Isn't the force The force exerted on the 11th car is moving 10 cars, not just one.
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    Gravitational Forces

    Homework Statement So finals is coming up and I was reviewing my notes, when I read that according to Netwon's Third Law gravitational forces (Fg) should be equal between to objects like the sun and the Earth. So if the sun and earth have the same Fg toward each other, why doesn't the sun...
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    Oscillation and Period

    Homework Statement A mass attached by a light spring to the ceiling of an elevator oscillates vertically while the elevator ascends with constant acceleration. Is the period greater than, less than, or the same as when the elevator is at rest Homework Equations T=2pi * sqrt(m/k) The...
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    Amplitude and period

    Homework Statement A mass oscillating on a given spring has a period of 2s. The spring is now stretched to have an oscillation amplitude that is twice its original amplitude. Which of the following is true? A The period is 0.5 s. B The period is 1 s. C The period is 2 s. D The...
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    Confusion with work and constant velocity

    Homework Statement So I'm confused about work and constant velocity. In a sailboat example, if the boat is going at constant velocity then there is no acceleration, therefore no net Force and no work. However, let's say there is an elevator being pulled upward by a pulley at constant...
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