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physics question
Started by slyloxy
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http://physicsforums.com/archive/index.php/t-101357.html
(See Number 1)
Incase the above doesn't make too much sense:
Easiest way is to find the acceleration of the object, then use kinematics to solve for v(final). We know that F = ma = E * q. Notice the units when we divide "q" by "m" = C/kg. So the question is, how can we derive those units from the given?
Since we know the charge density (C/m) and the mass density (kg/m), we can come up with C/kg by (charge density) / (mass density) = C/kg. Therefore, acceleration = 100V/m * (4e-5 / 1e-1 ) ==> 4e-2 m/s^2.
Finally, use the kinematic equation v(f)^2 = v(i)^2 + 2(a)(x). So, v(f) = ( 2 x 4e-2 x 2)^0.5 ==> 0.4 m/s answer.
EDIT: I think.
(See Number 1)
Incase the above doesn't make too much sense:
Easiest way is to find the acceleration of the object, then use kinematics to solve for v(final). We know that F = ma = E * q. Notice the units when we divide "q" by "m" = C/kg. So the question is, how can we derive those units from the given?
Since we know the charge density (C/m) and the mass density (kg/m), we can come up with C/kg by (charge density) / (mass density) = C/kg. Therefore, acceleration = 100V/m * (4e-5 / 1e-1 ) ==> 4e-2 m/s^2.
Finally, use the kinematic equation v(f)^2 = v(i)^2 + 2(a)(x). So, v(f) = ( 2 x 4e-2 x 2)^0.5 ==> 0.4 m/s answer.
EDIT: I think.
Cool, exactly how I figured I'd do it. 👍
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They're not going to test you with overly specific numbers... but you might get a passage that tests your ability to relate the concepts of electric fields with kinematics and maybe circuits, all in a single passage. Its just a matter of being able to apply different concepts towards a single unified problem.
Some of the practice tests have questions like this. If youre ever stuck on a physics problem and its the last problem for you to complete, just think of what category it is in (electrostatics), and write down the equations you remember (f=ma, f=Eq, E=v/m, U=qV), and then write down what you know (E=#, m=#, q=#) and then try to put it together. With my major I've had a TON of physics, which means a lot of tests where I have no clue where to start, and this method usually works out.
