The particle velocities in the beam have the same direction and lie in the
range from v to v + ∆v (∆v ≪ v). There are n particles in the unit volume of
the beam, and the mass of each particle is m.
a. During the time τ, the force F acts on the particles in the direction of their
motion. Determine the velocity interval and the number of particles per unit
volume after the force is applied.
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b. Determine the velocity interval and the number of particles per unit volume
after passing through the area where the force F was acting on the particles
at a distance l along the direction of motion.