Which statement best describes the role of folders in your operating system?
a. folders scan your hard disk for errors and then provide a follow-up report.
b. folders make it possible to retrieve recently deleted files.
c. folders your computer boot up.
d. folders allow you to organize and maintain files.

In a game of pool, ball a is moving with a velocity v0 of magnitude v0 = 15 ft/s when it strikes balls b and c, which are at rest and aligned as shown. knowing that after the collision the three balls move in the directions indicated and assuming frictionless surfaces and perfectly elastic impact (that is, conservation of energy), determine the magnitudes of the velocities va, vb, and vc.