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# A positive charge of 5.30 μC is fixed in place. From a distance

### Customer Question

A positive charge of 5.30 μC is fixed in place. From a distance of 4.60 cm a particle of mass 5.60 g and charge +3.30 μC is fired with an initial speed of 80.0 m/s directly toward the fixed charge. How close to the fixed charge does the particle get before it comes to rest and starts traveling away?
Submitted: 2 years ago.
Category: Homework
Expert:  akch2002 replied 2 years ago.
Customer: replied 2 years ago.
One hour :-)
Customer: replied 2 years ago.

Well actually as soon as possible ;-)
Expert:  akch2002 replied 2 years ago.
OK. I will reply it shortly.
Customer: replied 2 years ago.
Thank you Sir.
Expert:  akch2002 replied 2 years ago.

A positive charge of 5.30 μC is fixed in place. From a distance of 4.60 cm a particle of mass 5.60 g and charge +3.30 μC is fired with an initial speed of 80.0 m/s directly toward the fixed charge. How close to the fixed charge does the particle get before it comes to rest and starts traveling away?

As 3.3micro-coulomb charge reaches 5.3 micro coulomb charge, its kinetic energy will be converted into potential energy. At the nearest point, all the kinetic energy will be converted into potential energy.

Kinetic energy = (1/2)mv^2 = (1/2)*(5.6/1000)*80^2 = 17.92 J

Potential energy = Q1Q2/(4pi*ε0*R) were R is the distance between Q1 andQ2.

Hence, 17.92 = (5.3*10^-6)*(3.3*10^-6)/[4pi*(1/36pi*10^9*R)] = 0.15741/R

Or, R = (0.15741/17.92)*100 = 0.8784 cms.

So the minimum distance will be 0.8784 cms when 3.3 micro-coulomb charge will start reverting back.

I hope it will help. Kindly let me know any questions if you have.

Customer: replied 2 years ago.

Hello,

Thanks for your answer but it seems to be wrong as the online system where i have to post the result says it is not correct. I have also tried to post rounded variants of the figure you gave [0.8784] but it seems it is not the right answer :-(
Can you please take another look at it ?
Expert:  akch2002 replied 2 years ago.
I have checked calculations and find the minimum distance to be 0.8784 cms.
Customer: replied 2 years ago.

Sorry but the answer is still incorrect. The one in the online database is surely right. Did you take into consideration that they asked specifically :

How close to the fixed charge does the particle get before it comes to rest and starts traveling away?

Please fix this for me I am desperate ;-)
Expert:  akch2002 replied 2 years ago.
Try 0.44cms as potential energy is taken as 2 times q1q2/4piepsion0*R. In that case distance will be reduced to half of earlier calculated.
Expert:  akch2002 replied 2 years ago.
Sorry, potential energy is actually(1/2) times q1q2/4pi*epsilon0*R=17.92/2 J and minimum distance will be 1.756, say 1.76cms.Try it.
Customer: replied 2 years ago.

Wrong again ... Maybe you got the formula right this time but the calculations are off ?
Expert:  akch2002 replied 2 years ago.
KE = (1/2)MV^2 = 0.5*(5.6/1000)*80^2 = 17.92J

PE = (1/2)Q1Q2/(4pi*ε0*R) = 0.5*5.3*10^-6*3.3*10^-6*9*10^9/R = 0.078705/R

R = (0.078705/17.92)*100 = 0.4392, say 0.44 cms. Try it.
Customer: replied 2 years ago.

We already got that answer before and it did not work .... The calculations are correct though, so maybe its the formula ?
Expert:  akch2002 replied 2 years ago.
You relist it so that some other expert will try it and help you. Thanks.
Customer: replied 2 years ago.
ok thank you and sorry for wasting your time ...
Customer: replied 2 years ago.
Expert:  Sandhya replied 2 years ago.

A positive charge of 5.30 μC is fixed in place. From a distance of 4.60 cm a particle of mass 5.60 g and charge +3.30 μC is fired with an initial speed of 80.0 m/s directly toward the fixed charge. How close to the fixed charge does the particle get before it comes to rest and starts traveling away?

Please try and let me know.

Thanks
Customer: replied 2 years ago.

Can you send me some details of the calculations please ? thxs
Expert:  Sandhya replied 2 years ago.

Sure, I will send. Is answer correct or not?

Let me know.

Thanks
Customer: replied 2 years ago.

Oh well ok I will let you know but a bit later because I am doing this for my friend who is not online at the moment ;-) I will let you know as soon as I know :)
Expert:  Sandhya replied 2 years ago.
okay, I will wait
Expert:  akch2002 replied 2 years ago.
Answer by Sandhya seems to be correct as we have to consider potential energy in beginning also.
Expert:  Sandhya replied 2 years ago.
Thanks, XXXXX XXXXX type and send detailed solutions by morning time.

A positive charge of 5.30 μC is fixed in place. From a distance of 4.60 cm a particle of mass 5.60 g and charge +3.30 μC is fired with an initial speed of 80.0 m/s directly toward the fixed charge. How close to the fixed charge does the particle get before it comes to rest and starts traveling away?

Please try and let me know.

Thanks
Expert:  Sandhya replied 2 years ago.
You can view this answer by clicking here to Register or Login and paying \$3.
Sandhya, Tutor
Category: Homework
Satisfied Customers: 3629
Experience: I have several years of teaching experience.

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