2013-01-29, 10:33 PM
(This post was last modified: 2013-01-30, 01:50 AM by Marksman Bryan.)
I don't know what I'm doing wrong.
A proton is projected in the positive x direction into a region of uniform electric field E = -5.30e5 i N/C at t = 0. The proton travels 6.90 cm as it comes to rest.
Acceleration = -5.07e13
Initial Velocity = 2644779
Determine the time interval over which the proton comes to rest.
?????
I don't understand.
xf = xi + vi*t + 1/2*a*t^2
0.069 = 0 + 2644779*t - 2.535e13*t^2
-2.53e13*t^2 + 2644779*t - 0.069 = 0
a = -2.535e13
b = 2644779
c = -0.069
x = [ -2644779 +/- sqrt(2644779^2-4*-2.535e13*-0.069) ] / (2*-2.535e13)
gives imaginary solution... using numbers that are correct/given.
This is just a simple quadratic problem, right?
Or am I missing something and I'm somehow supposed to use the E field? Professor cancelled the second lecture (which is where we were supposed to discuss E fields and whatnot), but this homework is still due tonight.
bonus:
how would one go about solving a problem like this? The textbook is confusing me and I don't quite understand where some variables come from.
A +2 microCoulomb charge is located at the origin. What is the magnitude of the E field from theis charge at x = 2 m (on the x-axis)?
thanks [MENTION=1984]xXiris[/MENTION];!
EDIT:
I kept getting 2.61e-8 when I messed around with the signs, and I got frustrated so I started guessing. Around 4.8e-8 webassign said I was within 10% of the answer.. so I looked back and wondered if I doubled 2.61e-8. It worked.
The answer is 5.22e-8. I realize I was off by a multiple of two and I don't have the brainpower left tonight to see where I went wrong. If anyone else wants to point out the mistake while I sleep, be my guest. I'll look it over tomorrow.
A proton is projected in the positive x direction into a region of uniform electric field E = -5.30e5 i N/C at t = 0. The proton travels 6.90 cm as it comes to rest.
Acceleration = -5.07e13
Initial Velocity = 2644779
Determine the time interval over which the proton comes to rest.
?????
I don't understand.
xf = xi + vi*t + 1/2*a*t^2
0.069 = 0 + 2644779*t - 2.535e13*t^2
-2.53e13*t^2 + 2644779*t - 0.069 = 0
a = -2.535e13
b = 2644779
c = -0.069
x = [ -2644779 +/- sqrt(2644779^2-4*-2.535e13*-0.069) ] / (2*-2.535e13)
gives imaginary solution... using numbers that are correct/given.
This is just a simple quadratic problem, right?
Or am I missing something and I'm somehow supposed to use the E field? Professor cancelled the second lecture (which is where we were supposed to discuss E fields and whatnot), but this homework is still due tonight.
how would one go about solving a problem like this? The textbook is confusing me and I don't quite understand where some variables come from.
A +2 microCoulomb charge is located at the origin. What is the magnitude of the E field from theis charge at x = 2 m (on the x-axis)?
thanks [MENTION=1984]xXiris[/MENTION];!
EDIT:
I kept getting 2.61e-8 when I messed around with the signs, and I got frustrated so I started guessing. Around 4.8e-8 webassign said I was within 10% of the answer.. so I looked back and wondered if I doubled 2.61e-8. It worked.
The answer is 5.22e-8. I realize I was off by a multiple of two and I don't have the brainpower left tonight to see where I went wrong. If anyone else wants to point out the mistake while I sleep, be my guest. I'll look it over tomorrow.