Two marbles are rolling along parallel tracks (which may or may not be inclined). A stroboscopic photograph showing a top view of the positions of the marbles at equally spaced instants of time looks like this:

At what instant(s) of time do the marbles have the same instantaneous velocity?
A) At time $t_{B}$
B) At time $t_{G}$
C) At both $t_{B}$ and $t_{G}$
D) Some instant between $t_{C}$ and $t_{D}$
E) Some instant between $t_{D}$ and $t_{E}$
F) Roughly time $t_{D}$

Question

Two marbles are rolling along parallel tracks (which may or may not be inclined). A stroboscopic photograph showing a top view of the positions of the marbles at equally spaced instants of time looks like this:

At what instant(s) of time do the marbles have the same instantaneous velocity?
A) At time $t_{B}$ 
B) At time $t_{G}$ 
C) At both $t_{B}$ and $t_{G}$ 
D) Some instant between $t_{C}$ and $t_{D}$ 
E) Some instant between $t_{D}$ and $t_{E}$ 
F) Roughly time $t_{D}$

Quizplus · Accepted Answer

The Answer of Two marbles are rolling along parallel tracks (which may or may not be inclined). A stroboscopic photograph showing a top view of the positions of the marbles at equally spaced instants of time looks like this:

At what instant(s) of time do the marbles have the same instantaneous velocity?
A) At time $t_{B}$ 
B) At time $t_{G}$ 
C) At both $t_{B}$ and $t_{G}$ 
D) Some instant between $t_{C}$ and $t_{D}$ 
E) Some instant between $t_{D}$ and $t_{E}$ 
F) Roughly time $t_{D}$

Two Marbles Are Rolling Along Parallel Tracks (Which May or May