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• Users: Loppyfoot
• In Introductory Physics Homework Help
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1. Question on Surface Integral and Flux

Could I use, (3,-1,0)x(0,0,-1)?
2. Question on Surface Integral and Flux

Alright, so the corss product of two vectors will give me a vector that is perpendicular to the plane (which is in the direction that I want). I'm not sure what these vectors would be? How do I know what vectors to cross?
3. Question on Surface Integral and Flux

Would I compare triangles in the xy-plane?
4. Question on Surface Integral and Flux

Homework Statement I have a coordinate system, (x,y,z). There is a uniform-magnetic-field of 2.0 T that exists along the direction of the y-axis. There is a rectangular plane bounded by the points (3,0,0),(0,1,0),(0,1,1),(3,0,1). Calculate how much flux is traveling through the rectangular...
5. Electric Potential Question

Homework Statement Which of the following statements about the electric potential inside a metal object are correct? Check all that apply. The potential at any point inside a metal at equilibrium is equal to the potential at the surface, which may be nonzero. The potential is the same...
6. Which of the following

Which of the following... Homework Statement In a collision between an electron and a hydrogen atom, it is useful to select both objects as the system because: A. The total momentum of the system does not change during the collision B. The forces the objects exert on each other are...
7. Finding Kinetic Energy of a Collision

Homework Statement A 900 kg car moving east at 31 m/s runs head-on into a 2800 kg truck moving west at 15 m/s. The vehicles stick together. Use the concept of the center-of-momentum frame to determine how much kinetic energy is lost. Homework Equations Kf= Ki(car) + Ki(truck) K=...
8. Rotational Velocity Problem

That's not the equation? Then what equation would I use to represent the rod with moment of inertia?
9. Rotational Velocity Problem

Moment of Inertia= mr^2. Sorry.
10. Rotational Velocity Problem

Homework Statement A thin uniform-density rod whose mass is 3.8 kg and whose length is 3.0 m rotates around an axis perpendicular to the rod, with angular speed 34 radians/s. Its center moves with a speed of 10 m/s. (a) What is its rotational kinetic energy? (b) What is its total kinetic...
11. Vertical Spring Potential Energy?

Homework Statement Say I have a vertical spring, with a mass attached to the bottom of the spring, and the spring is attached to the ceiling. Say I push up on the mass compressing the spring, and then I release the spring from rest. Do I need to take into account the gravitational...
12. Classic Football Kick Problem

You could square both sides, and then we can work it out from there?
13. Classic Football Kick Problem

Are there any sin and cosine laws that would help, like the square of sin added to the square of cosine equalling one?
14. Classic Football Kick Problem

hmm. what did you come out with?
15. Classic Football Kick Problem

Ok i'll, as well.
16. Classic Football Kick Problem

I don't see what you're getting at. I know there are these two equations, I need to solve a variable deltat to get one variable left. After I try to do that step, I get a ridiculous equation that I need to solve for theta. Is there any other process of doing this problem?
17. Classic Football Kick Problem

I attempted to solve for deltat, but when I plugged delta t from the 2nd equation into the first equation i get a long equation with costheta- costhetasintheta. I'm confused
18. Classic Football Kick Problem

the higher angle would be when the ball strikes the top of the post.
19. Classic Football Kick Problem

Because the problem does not supply deltat, where should that number come from? 54m/27m/s= 2s?
20. Classic Football Kick Problem

my answers don't seem to be working. I get for the largest angle possible: 54= 27^2sin(theta)^2/ (9.8) = .8520=sintheta= 58 degrees. would that be correct for the larger angle?
21. Classic Football Kick Problem

u stands for velocity, correct? and how do I differentiate between the largeer and smaller angles?
22. Classic Football Kick Problem

hmm. I'm still confused. Would I do 54= 27sin(theta)*deltat + .5(-9.8)deltat and then solve for theta?
23. Classic Football Kick Problem

Homework Statement A football kicker can give the ball an initial speed of 27 m/s. He is 54 m from the goalpost which has a crossbar 3.37 m high. (a) What is the largest angle of elevation that he can kick the football and score a field goal? (b) What is the smaller angle of elevation that...

25. Position of an object after a certain amount of time?

So, the velocity would be <0,0,-5> since it is in the -z direction?
26. Position of an object after a certain amount of time?

Ok, xf = xi + vi*t + 0.5*a*t^2 xf = <0,0,0>m + <0,0,5>*20 + 0.5*(<0,0,-30>N/200kg)*(20s^2)
27. Position of an object after a certain amount of time?

So I'll use: deltax = vi*t + 0.5*a*t^2. I plug in the proper values, and I don't get the correct answer. I am unsure of where I am going wrong. The initial position is, <0,0,0>, so I don't need to worry about that.
28. Position of an object after a certain amount of time?

Homework Statement Your location is at the origin. When an object passes you, it is traveling 5 m/s in the −z direction. If the object's mass is 200 kg, and the net force on the object remains constant at ‹ 0, 0, −30 › N, what is the position of the object 20 seconds after it passes you...
29. How to Change a Horizontal Vector to Move in a 45 degree angle

Ok, So the x-component is 1e7cos(45), where the y-component is 1e7sin(45), so the hypotenuse is the vector that makes up both of these components, which allows the object to move in the direction that is 45 degrees from the horizontal. Is that a decent understanding? Thanks for your help.
30. How to Change a Horizontal Vector to Move in a 45 degree angle

Where do you get the formula: vx = speed * sin (45)? Thanks.
31. How to Change a Horizontal Vector to Move in a 45 degree angle

Ok, I get it, and I got it working. Thanks for your help.
32. How to Change a Horizontal Vector to Move in a 45 degree angle

Homework Statement I am using vPython, and object moves in a +x direction with a vector of <1e7,0,0>m. I need to now change the vector so that it now moves in the same +x direction, but also moving in the northeast direction at an angle of 45 degrees. The Attempt at a Solution I...
33. Basic Concept Physics Question

Homework Statement An object is moving in the +z direction. Which, if any, of the following statements do you know must be false? Check all that apply. 1. velocity of z is zero. 2. The net force on the object is in the -z direction. 3. The net force on the object is zero. 4. The net...
34. Simple Power/Work problem

I got it. Since a Joule is a N*m, and Power is a N*m/s; I just multiple the 1000N by 3m/s to get the power. Thanks brain!
35. Simple Power/Work problem

Homework Statement What is the power being exerted by a force of 1000. N on a car traveling at 30. m/s? (Assume that force and speed are in the same direction, and treat all numbers as positive.) Homework Equations Power = J/s Work =F*d
36. How do I find tangential acceleration?

Homework Statement You are designing a centrifuge to spin at a rate of 15,180 rev/min. (a) Calculate the maximum centripetal acceleration that a test-tube sample held in the centrifuge arm 15.2 cm from the rotation axis must withstand. I found (a) by the formula v2/r and got approximately...
37. Position and Velocity Vectors

I think I figured it out. I applied one of the 4 kinematic equations, and then I should be able to get the rest from there. EDIT: I got a and b, but how would I go about getting c and d?
38. Position and Velocity Vectors

If the acceleration is constant, doesn't that mean that the velocity is changing at a constant rate?
39. Position and Velocity Vectors

How should I implement that equation into part a), if I do not know the acceleration vectors yet?

How would I find this in i and j vectors?
41. Position and Velocity Vectors

Jeez, I cannot seem to get this! I have been trying to get it all night.
42. Position and Velocity Vectors

Homework Statement A particle moves in the xy plane with constant acceleration. At t = 0 the particle is at rvec1 = (3.7 m)i + (3.4 m)j, with velocity vvec1. At t = 3 s, the particle has moved to rvec2 = (9 m)i − (1.9 m)j and its velocity has changed to vvec2 = (5.4 m/s)i − (6.5 m/s)j. (a)...
43. Unit Vector Help

Got it. Thanks man!

I drew the diagram, but I couldn't find a right angle anywhere. Where is this right angle? I need to find the i and j unit vectors, but how?

Homework Statement A stationary radar operator determines that a ship is 12 km south of him. An hour later the same ship is 10 km southeast. If the ship moved at constant speed and always in the same direction, what was its velocity during this time? This is so easy but I am just so...
46. Unit Vector Help

So would it be 4i - 3j? On my webassign homework, it has to be a single numerical value.
47. Unit Vector Help

Homework Statement Find the magnitude and direction of A + B for the following vectors. A = -4 i - 1 j, B = 8 i -2 j How do I find the magnitude of A+B, and also the degree clockwise from the +x direction?
48. Mag and Direction of 3d Vectors

English please? is Az, 4k? Also, how do I find the direction in xy plane counter clockwise from the +x axis?
49. Mag and Direction of 3d Vectors

Homework Statement Find the magnitude and direction of the following vectors. C = -2 i - 9 j + 4 k I found that the magnitude was 10. By using the square root of (4+9+4). I don't know how to find: Angle from +z-axis and the direction in xy plane counter clockwise from the +x...
50. A cop chasing a car

I am having trouble with the fact that is starts 1.72s behind.