# Search results

1. ### Force on electron from current-carrying wire

Homework Statement http://img236.imageshack.us/img236/5369/physxn6.png [Broken] Homework Equations F = IL x B F = QV x B The Attempt at a Solution Since I know I, L, Q, and V, I tried to work those into the two force equations... but I got no where. They dont give me B.
2. ### Tricky torque problem

Work is the change in kinetic energy. KEf - KEi, but since its at rest in the beginning, its KEf - 0, which is just w=KEf. Remember to consider rotational kinetic energy, because it is rotating. Good luck to you both!
3. ### Tricky torque problem

they give you 118 rpm. You have to convert that to angular velocity using factor label. You have time and final angular velocity, so you can find angular acc. using Vf = Vi + at where Vf=final angular vel, Vi = initial angular vel (which is 0 in this case), a=angular acc, and t=time. then...
4. ### Calculating final Velocity

well then i guess your initial approach is correct. the equation I gave might not work cuz i didnt read the part that said "avg velocity". I think your -61 is correct
5. ### Calculating final Velocity

I dont know why they gave you impulse, you can solve the problem with this equation: Vf = Vi + at where Vf=final velocity, Vi=initial velocity, a=acc. and t=time. Remember - the acc. is .8/.462 because F=ma, so a=F/m. Good luck!

Yes.
7. ### Frictionless Surface

Newton's 3rd law tells us that when you punch the wall, the wall punches back equally. In other words, with equal force. In other words, you don't punch the block with any more force than the wall punches you with. In other words, your punch's force and the wall's punching force are equal. So...
8. ### Two objects - when do they meet?

Homework Statement An object is thrown downward with an initial speed of 4 m/s from a height of 99 m above the ground. At the same instant, a second object is propelled vertically from ground level with a speed of 25 m/s. The acceleration of gravity is 9.8 m/s^2. At what height above...
9. ### Position when 2 objects pass each other

What I did didn't work. I kind just mushed stuff together. I might as well have said "I didnt know where to start" because I didnt.
10. ### Packaged dropped from Hot Air Balloon

well a is -9.8 because of gravity. Vi is 2.6, but its the opposite direction of falling. So what do I do with it? d is 19 m. I dont know how to use that equation because the Velocity is upward, but the object is falling DOWN.
11. ### Please help - Rotational Kinetic Energy of Moving Wheel

First of all, you dont need to make a theoretical velocity because they cancel out in the end. Now... (2)(1/2 I w^2) + (1/2 m v^2) (2)(1/2) is 1. You know that w=v/r, so plug in v/r for w, and you get I(v/r)^2 + (1/2 m v^2) You know I, r, and m, so you get ((.08)V^2)/.3 + (1/2)(74)V^2 Do...
12. ### Please help - Rotational Kinetic Energy of Moving Wheel

Total KE in this case is 2KEr + KEt, where KEr is rotational kinetic energy and KEt is translational/linear kinetic energy. Because the bike itself as a whole is moving linearly, it has KEt. And since there are two wheels, there is KEr - but 2KEr because of the two wheels. So the total...
13. ### Position of toy moving on straight track

Homework Statement The position of a toy locomotive moving on a straight track along the x-ais is given by the equation x = t^6 - 6t^2 + 9t where x is in meters and t is in seconds. The net force on the locomotive is equal to zero when t is equal to _______? Answer in units of...
14. ### Packaged dropped from Hot Air Balloon

Homework Statement A Hot air balloon is traveling vertically up- ward at a constant speed of 2.6 m/s. When it is 19 m above the ground, a package is released from the balloon. The acceleration of gravity is 9.8 m/s^2. After it is released, for how long is the package in the air? Answer...
15. ### Position when 2 objects pass each other

Homework Statement An object is thrown downward with an initial speed of 4 m/s from a height of 99m above the ground. At the same instant, a second object is propelled vertically from the ground level with a speed of 25 m/s. The acceleration of gravity is 9.8 m/s^2. At what height above the...
16. ### Newton's Second Law-Pulley problem

Perhaps your Force of Friction is incorrect? Double check and make sure all the numbers given is the same, and get back to me.
17. ### Newton's Second Law-Pulley problem

Ok. Well, do you see how you can use my demonstration to solve for acceleration as well? Put T on one side of both italicized equations, set them equal to each other, then solve for acceleration.
18. ### Newton's Second Law-Pulley problem

Assuming you're looking for tension... http://www.geocities.com/chmode12/pulley.JPG
19. ### Newton's Second Law-Pulley problem

What are you looking for? Tension?
20. ### Finding Kinetic Energy of Person Spinning on Chair w/ Weights

Alright. But just fyi, I know it cant be the same I because the r changes, but the problem says to just assume its the same. I used the same I for initial and final to get the wf, and it was correct, so i know I is same initial and final. Anyways, heres the problem: A student sits on a...
21. ### Finding Kinetic Energy of Person Spinning on Chair w/ Weights

Ahh, sorry, I suppose I should have included this information in the main thread. My bad. Well I is the same for initial and final, which is 8. Therefore, Initial I = 8 Final I = 8 Initial w = .7 Final w = 1.15 So I did: (1/2)(I)(wf)^2 - (1/2)(I)(wi)^2 = (1/2)(8)(1.15)^2 -...
22. ### Finding Kinetic Energy of Person Spinning on Chair w/ Weights

How do you find the Kinetic Energy of a person spinning on a chair with 2 equal weights on each arm? A specific problem asks what the change in KE is if he moves his originally extended arms inward. I tried doing (1/2)(I)(wf)^2 - (1/2)(I)(wi)^2 where wi is initial angular velocity and wf...
23. ### Door Torque Question - Solved Question

I didnt read your entire thread, but I have come across this question before. The best way to approach this problem is to get a calculator or book, and hold it with two fingers at where the top hinge would be holding a door. You will notice the book is hanging at an angle. Now with your...