The firing sequence in a drivage is shown. The charge per hole for Sections 1, 2, and 3 are 2.0 kg, 3.0 kg, and 1.0 kg, respectively, and the delay between each section is 25 milliseconds. The maximum charge per delay, in \(kg\), is
Show Hint
Work out the total charge fired in each section, then check whether the 25 ms gap between sections is enough to keep them on separate delays instead of adding together.
Step 1: Understanding the Concept.
Maximum charge per delay (MCD) is the heaviest single explosive charge that detonates at one instant during a blast. It matters because ground vibration depends on MCD, not on the total explosive used in the whole round, so spreading a blast over many delays is how large rounds are fired without shaking the ground too hard.
Step 2: Key Formula or Approach.
Charge per section $=$ number of holes in that section $\times$ charge per hole. Two sections combine into one effective delay only if the time gap between them is small enough (about 8 ms or less) that the ground cannot tell them apart. Here the gap is 25 ms, larger than that limit, so each section is its own delay and MCD is just the largest section total.
Step 3: Detailed Explanation.
From the drawing, the inner diamond (Section 1) holds 4 holes, the middle ring (Section 2) holds 4 holes, and the outer ring nearest the drive boundary (Section 3) holds 8 holes.
Section 1 total $= 4 \times 2.0 = 8.0$ kg.
Section 2 total $= 4 \times 3.0 = 12.0$ kg.
Section 3 total $= 8 \times 1.0 = 8.0$ kg.
A common mistake is to add all three sections together to get $8.0+12.0+8.0=28.0$ kg (option D), treating the whole round as one delay, but that ignores the 25 ms gap that keeps the sections separate. Another mistake is misreading the hole counts to land on $20.0$ kg (option C), which does not match the actual layout. Option (A), $8.0$ kg, is only the value of Section 1 or Section 3 alone, not the largest of the three.
Since the sections fire on separate delays, we only need the single biggest section, which is Section 2 at $12.0$ kg.
Step 4: Final Answer.
The maximum charge per delay is $12.0$ kg, coming from Section 2 (4 holes at 3.0 kg each), which corresponds to option (B).
