Answer
The buoyant forces are equal. The gravel-filled life preserver is ineffective.
Work Step by Step
Both preservers are the same size, and displace the same volume of water when submerged. The buoyant forces on each are equal.
The amount of buoyant force exerted on the preserver is less than the weight of the gravel-filled preserver, so the preserver would sink. We don't recommend using it.
