<span>A. No sound is heard
A*sin(wt)+(-A)*sin(wt)=0 - no sound
</span>
We assume

(acceleration is constant. We apply the equation

where s is the distance to stop

. We find the acceleration from this equation

We know the acceleration, thus we find the distance necesssary to stop when initial speed is

The answer is
h: sB and Sb
hd : sb
hr : SB