1) An infinitely long line of charge has linear charge density 5.50×10−12 C/m. A proton (mass 1.67×10−27 kg , charge 1.60×10−19 C ) is 17.0 cm from the line and moving directly toward the line at 1000 m/s.
a) Calculate the proton’s initial kinetic energy.
b)How close does the proton get to the line of charge?
5 Answers

A) Protons mass: 1.67 x 10^27kg
V= 1000 m/s
K.E= 1/2*m*v^2
=0.5*1.67*10^27kg*(1000)^2
= 8.35*10^22 J
A) The proton’s initial kinetic energy is 8.35*10^22 J

kinetic energy = 0.5mv^2
K.E= 0.5* 91.67*10^27 ) *100^2

For a given velocity, maximum range R = v^2 / g and for a given range this is the minimum velocity => Minimum velocity, v = √(Rg) = √(98*9.8) = 31 m/s => Minimum KE = (1/2)*(0.8)*(31) J = 12.4 J Average force = 12.4/2 = 6.2 N You can use this method to work out the other two cases.

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brandon, “How long does the proton get to the line of charge? ” Is English your second language? This question makes no sense.

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K.E of proton =0.5mv^2= 8.35*10^22 J
A) The proton’s initial kinetic energy is 8.35*10^22 J
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Electric field due to a line of charge = E=2k*lembda/r
dU = Edr= (2k*lembda/r)dr
Potential difference = U2U1 = integral (2k*lembda)ln(r2/r1)
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Suppose proton stops at x m from line of charge
Work done by electric field = kinetic energy
work =q(U2 U1)=KE
1.6*10^19*(2k*lembda)ln(r2/r1)=8.35*10^…
(2k*lembda)ln(r2/r1) = 8.35*10^22 /1.6*10^19
ln(r2 / r1) = – 5.21875*10^3 / 2k*lembda
ln(r2/r1) = – 5.21875*10^3/2k*lembda
ln(r2/r1) = – 5.21875*10^3/2*9*10^9*5.5*10^12
ln(r2/r1) = – 0.0527146
ln(r2 /r1) = 0.0527146
(r2 /r1) = 0.9486
r2 = 0.17 *0.9486=0.16127m
B) The proton gets up to 16.127 cm or 0.16127 m from the line of charge
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