a 1.75kg pistol lies at rest on an essentially frictionless bench. it accidentally fires and shoots a 25 gram bullet parallel to the bench. How far has the bullet moved by the time the gun has recoiled 2.60mm?

the velocityies of the bullet and the gun are proportional to the ratio of masses.

Vbullet/vgun= massgun/massbullet

now, in the same time, the distances are proportional to velocities, so

distancebullet/distancegun= massgun/massbullet

so go figure.