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[Prologue]

Did a practice test but I would like to understand these two questions a bit more. I know the answers to both but that doesn't mean anything if i don't get it. Any help would be appreciated. Tutoring center closed tomorrow.

A very small 4.8-g particle carrying a charge of +9.9 μC is fired with an initial speed of directly toward a second small 7.8-g particle carrying a charge of + The second particle is held fixed throughout this process. If these particles are initially very far apart, what is the closest they get to each other? (k = 1/4πε0 = 9.0 × 109 N • m2/C2)

Two tiny beads, each of mass 3.2 g, carry equal-magnitude charges. When they are placed 6.4 cm apart and released in outer space, they begin to accelerate toward each other at 538 m/s2. What is the magnitude of the charge on each bead? (k = 1/4πε0 = 9.0 × 109 N • m2/C2)

 

[Beaniedude]

What exactly don't you understand about the questions? Would you mind showing us the working you've done? Maybe then we can focus on what you don't understand.

 

[Dryk]

The first question is an energy balance question:
Ki + Pi = Kf + Pf
Assuming that there's a point where they begin to move apart again, Kf = 0
If they're very far apart you can assume that Pi = 0
Then you can solve for the radius at which Pf = Ki


The second question gives you masses and an acceleration, so you can determine the force on each object and then solve Coulomb's Law for the charge.

 

[Prologue]

What exactly don't you understand about the questions? Would you mind showing us the working you've done? Maybe then we can focus on what you don't understand.

Its been over a year since I've taken physics 1. All the other questions I was able to answer but these two seem to borrow concepts from physics 1 so I'm a bit clueless.

Dryk, so for the second question, solve for force=ma and then solve for the charges given coulombs law since I have the force? Thats what I'm doing but I'm not getting 890 nC which is the answer.

F= ( 3.2g)(538 m/s)
F=1721.5

F = kPp/(r²) and solve for P right?

 

[Dryk]

Dryk, so for the second question, solve for force=ma and then solve for the charges given coulombs law since I have the force? Thats what I'm doing but I'm not getting 890 nC which is the answer.

F= ( 3.2g)(538 m/s)
F=1721.5

F = kPp/(r²) and solve for P right?

You're forgetting to convert to kg when calculating the force

 

[psylah]

F= ( 3.2g)(538 m/s)
F=1721.5

F = kPp/(r²) and solve for P right?

That's a whole mess of letters smarty pants, and the only letters I needed to learn in school was U, S, and A.

 

[Hitokage]

You're forgetting to convert to kg when calculating the force

Yeah, one habit you should have is immediately converting any given unit to SI before moving forward, unless the constants you're working with dictate otherwise and you don't need to mess with them or you're sure you can get away with just being consistent.

 

[Prologue]

You're forgetting to convert to kg when calculating the force

Yeah, one habit you should have is immediately converting any given unit to SI before moving forward, unless the constants you're working with dictate otherwise and you don't need to mess with them or you're sure you can get away with just being consistent.

Thanks guys! All the other problems had SI units. Crossed my mind given the physics 1 gap.