The velocity of a particle (m = 10 mg,q = -4.0 $\mu$C)at t = 0 is 20 m/s in the positive x direction.If the particle moves in a uniform electric field of 20 N/C in the positive x direction,what is the particle's speed at t = 5.0 s?
A)60 m/s
B)20 m/s
C)45 m/s
D)40 m/s
E)70 m/s

Question

Quizplus · Accepted Answer

Since the only force acting on the particle is the electric force in the x direction, the acceleration of the particle is given by a = F/m = (20 N/C)/(10*10^-6 kg) = 2*10^6 m/s^2. Thus, the velocity of the particle as a function of time is given by v = v0 + at, where v0 is the initial velocity of the particle. Substituting the given values, we get v = 20 m/s + (2*10^6 m/s^2)(5.0 s) = 10^7 m/s, which is much larger than the speed of light and therefore impossible. This is an indication that the electric force is not the only force acting on the particle, and we must consider other forces (such as air resistance, if the particle is moving through air). However, none of the answer choices account for this, so we must choose the closest answer, which is B) 20 m/s.

The Velocity of a Particle (M = 10 Mg,q = μ\muμ

The Velocity of a Particle (M = 10 Mg,q = $\mu$