9/10/2018 11:59 PM 77.2/100 Gradebo Print E Caluutor ed Penck Table Question 5 o

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9/10/2018 11:59 PM 77.2/100 Gradebo Print E Caluutor ed Penck Table Question 5 of 9 University Physios Map dob presented by Sapling Leaming Two red blood cells each have a mass of 9.05 x 10* kg and carry a negative charge spread uniformly over their surfaces. The repulsion arising from the excess charge prevents the cells from One cell camies -2.30 pC and the other -2.90 pC, and each cell can be modeled as a sphere 3.75 x10 m in radius. If the red blood cells start very far apart and move directly toward each other with the same clumping together theed, wainta spreadwuleach need so thar they get cdose enough to just barely touch? Assume that is no viscous drag from any of the surrounding liquid Number m/s What is the maximum acceleration of the cells as they move toward each other and just barely touch? Number m/s Hint O Previous Gve Up & View Sonaer, Check Answer 0 Next 1"- 10

Explanation / Answer

when they are very far away, electric PE of system = 0

so PEi = 0

when they barely touch, distance between centers,

d = 2 r = 7.5 x 10^-6 m

Now PE = k q1 q2 / d = (9 x 10^9)(-2.30 x 10^-12)(-2.90 x 10^-12)/(7.5 x 10^-6)

PEf = 8 x 10^-9 J

so they just barely touch, vf = 0

Applying energy conservation,

PEi + KEi = PEf + KEf

0 + 2( m v^2 / 2) = 8 x 10^-9 + 0

(9.05 x 10^-14) v^2 = 8 x 10^-9

v = 298 m/s ........Ans

Now Fe = k q1 q2 / d^2 = 1.0672 x 10^-3 N

and a = Fe / m

a = 1.18 x 10^10 m/s^2 .......Ans

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