7. Friction, Inclines, Systems

A 4.0-kg box sits on a frictionless inclined plane that makes a 21° angle with the horizontal. It is held in place by a cord parallel to the plane. Calculate the tension in the cord.

A box and a solid disk, both of equal mass, are released from rest at the top of a frictionless inclined plane of length $L$ and angle $\theta$. The box slides down without rolling, while the disk rolls without slipping. How much sooner does the box reach the bottom of the incline than the disk?