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# A foam ball of mass 0.150 g carries a charge of -2.00 nC.  The ball is placed inside a...

lkehoe | Valedictorian

Posted May 13, 2013 at 4:28 PM via web

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A foam ball of mass 0.150 g carries a charge of -2.00 nC.  The ball is placed inside a uniform electric field, and is suspended against the force of gravity.  What are the magnitude and direction of the electric field?

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sciencesolve | Teacher | (Level 3) Educator Emeritus

Posted May 13, 2013 at 6:51 PM (Answer #1)

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You need to evaluate the magnitude and direction of electric field, using Coulomb's force, such that:

`E = F/q`

Since the problem provides the mass of foam ball, you need to replace the product `m*g` for F, such that:

`E = (m*g)/q => E = (0.150*10^(-3)*9.8)/(-2*10^(-9))`

`E = -0.735*10^6N/C`

Hence, E needs to point vertically downward because `q = -2*10^(-9)<0` and its magnitude is of `E = 0.735*10^6N/C.`

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