<p>here is the mc problem?</p>
<p>An electron is accelerated from rest for a time of 10^-9 sec by a uniform electric field that exerts a force of 8 times 10^-15 N on the electron.
The electric field is 50000 N/C.
The speed of the electron after it has accelerated for the 10^-9 sec is most nearly???</p>
<p>Answer is 10^7 m/s but how do arrive at this answer???</p>
<p>Interestingly enough, this problem appeared on one of my teacher’s tests, too.</p>
<p>Anyways:</p>
<p>You are given F and you are given a time. First, use F=ma to solve for the acceleration. You have a F and the mass of an electron is given to you (or at least should have been given to you). When you have your acceleration, use v=at (because initial velocity is 0).</p>
<p>By the way, on an AP exam, the electron mass is given to you; it’s impossible to solve this without knowing/being given electron mass.</p>
<p>Constants you should know beforehand:
1 e-=1.60X10^-19
mass of electron = 9.11x10^-31 kg</p>
<p>50000N/C x (1.60x10^-19 C) = 8.0 x 10^-15N</p>
<p>(8.0x10^-15N)/(9.11x10^-31 kg)=8.8x10^15 m/s^2.</p>
<p>(8.8X10^15 m/s^2)x(10^-9)=8.8x10^6 m/s, approximately equal to 10^7 m/s.</p>