# Search results

1. ### Static frictions and moving boxes on top of a box

ohh I didn't include that. Thanks, it makes sense!
2. ### Static frictions and moving boxes on top of a box

hmm so far.. m= mass of box and M=mass of cart. I assume the acceleration of the box and cart is the same. F(box)=force(friction)=umg=ma ug=a F(cart)=force done by you=Ma Substitute ug=a into the equation. u*g*M=Force so mass of the box doesn't matter?
3. ### 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
4. ### Calculate wavelength of electron

Thanks. So in addition to time dilation and length contraction, is this what you call momentum dilation?
5. ### 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
6. ### 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.
7. ### Conservation of energy and electrons in electric field?

sweet thanks a lot. what a tricky question
8. ### 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...
9. ### Monochromatic light and reflection

lol no. This was a practice exam and half the people got it wrong. I guess the teacher was just being tricky.
10. ### Monochromatic light and reflection

so perhaps the index of refraction does not matter?
11. ### 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.
12. ### Thin hair diffraction

I'm still a bit confused as to why the dot like patterns are horizontal. What is the black dot? Is that suppose to indicate a circular single slit? In the following picture, I'm confused as to how the picture on the left translate to the one on the right. As the diffraction pattern on the left...
13. ### 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
14. ### Thin hair diffraction

I believe so. The wavelets due to huygen's principle can still propagate at the edges of the hair. Do the wavelets propagate horizontally around the vertical hair? It just confuses because single slit oriented vertically produce vertical patterns. But hair doesn't and I am told it acts similar...
15. ### 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?
16. ### 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...
17. ### Center of mass: What would make the truck tipover?

hmm I don't quite understand. would the equation be x*3/120000=2.5? This would mean that the distance of the weight of the load would be ignored.
18. ### 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...
19. ### 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...
20. ### 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...
21. ### 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...
22. ### How do you calculate Center of mass

oh so that's it. How about if they just give you the x-coordinate in a system? exe: http://www.screencast.com/users/ntrinh3/folders/Jing/media/010db89d-7781-4262-aa79-57eaf706730f do you just add all of the x-coordinates and divide by how many points?
23. ### 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...
24. ### Calculating velocity of a block on a slope using work theorem

oh nvm. I stepped away from this problem and realized the angle between the work and force was wrong.
25. ### 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...
26. ### Which forces does work as a car brakes?

When a car brakes, isn't it in motion and using kinetic friction to stop, and not static friction? Static friction causes rolling motion in wheels, but there is no rolling motion so it skids. So shouldn't kinetic friction do work and not static? I'm a bit confused on the two concept.
27. ### 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...
28. ### Calculate the energy lost to friction

nvm I figured it out. .2*mgcos15*d and the d=h/sin15 :approve:
29. ### 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...
30. ### Calculation loss of energy due to friction?

sorry I meant that F(k) which is the force due to kinetic friction. The equation for work is FDcos(theta). They gave use the height so I calculated the distance of the slope by Pythagorean theorem which gives cos(15)*the height.