Homework Help: Newton's Laws and an electron of mass

1. Feb 1, 2008

nlb149

1. An electron of mass 9.11 x 10^-31 kg has an initial speed of 4.00 x 10^5 m/s. It travels in a straight line, and its speed increases to 6.00 x 10^5 m/s in a distance of 3.00 cm.
(a) Assuming its acceleration is constant, determine the force exerted on the electron.
N (in the direction of motion)
(b) What is the ratio of this force to the weight of the electron, which we neglected?

2. F=ma

2. Feb 1, 2008

cse63146

Use one of the kinematics equations to determine the accelartion

You have initial velocity, final velocity and distance.

3. Feb 1, 2008

Newton1Law

What you know is this, in 0.03 meters of travel you achieved an additional velocity of 2 x10^5 m/s. You also know that s=0.5*a*t^2 thus 0.03 = 0.5*s*t^2 (first equation).

Next you know that v=at and that the increase of velocity was 2x10^5, thus the time could be found by using 2x10^5 = a*t (second equation)

You have two equations with two unkowns, solve for "a" and "t" then use F=ma to get the Force in Newtons. Acceleration will be about 66.67m/s^2 and F about 6.07X10^-24.

Hope this helps.