A crate is sliding down a $30^{\circ}$ incline, picking up speed as it slides. Ignore air friction.
-(c) Which force listed does not actually act on the crate?
A) $\left|\vec{F}_{N}\right|$
B) $\left|\vec{F}_{g}\right|$
C) Both $\left|\vec{F}_{N}\right|$ and $\left|\vec{F}_{g}\right|$ (which are equal)
D) $\left|\vec{F}_{S F}\right|$
E) $\left|\vec{F}_{K F}\right|$

Question

Quizplus · Accepted Answer

The force $\left|\vec{F}_{S F}\right|$ (static friction) does not act on the crate because the crate is sliding, not stationary. Instead, kinetic friction $\left|\vec{F}_{K F}\right|$ acts on the crate.

A Crate Is Sliding Down A 30∘30^{\circ}30∘ Incline, Picking Up Speed as It Slides

A Crate Is Sliding Down A $30^{\circ}$ Incline, Picking Up Speed as It Slides