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**Question**

Assuming the electric potential difference between the inside and outside of a cell is 70 mV and the thickness of the region across which this exists is 7 nm,

**calculate the acceleration a chlorine ion would experience in the absence of other forces. In the absence of other forces how long would it be before it was travelling at the speed of light? Why does this not happen?**Chlorine has a molecular weight of around 35 g/mole, Avogadro’s number is 6.022 × 10^23 per mole, and the speed of light, c, is 3×108 m/s.

**Equations**

Conservation of energy

KE=1/2mv^2

E=qV=Work

1/2mv^2=qV -

**Attempt**

Am I finding the kinetic energy generated and then the mass through that? I'm a bit stuck. I assume that the speed of light is only given to compare the velocity of the chlorine once I get it.

Is the charge of the chlorine just -1e? = -1.6x10^-19C As it's a negative charge does that mean the ion is slowing down as it moves through the membrane (I assume this is wrong as the question talks about it nearing the speed of light). I also don't know how to bring the cell thickness into it - I can use it to calculate the electrical field, is that what it's for 7.0x10^-3V / 7x10^-9m = 1x10^6V/m?

The mass of the ion is 35g/mole /6.022x10^23 = 5.8x1-^23g.

v^2 = (-1.6x10^-19C x 0.7V)/(0.5 x 5.8x1-^23g) - Definitely wrong as that would give me a negative number and I need to find the square root.

It's probably a really easy question but I'm stumped. I'd appreciate some help just to get me going :) and to better understand what is going on.