Convoy Fuel and Timing Decision
A convoy of eight loaded trucks must move from a depot to a forward post and return the same day. The one-way distance is 240 km. Each truck has a 100-litre tank and burns diesel at 1 litre per 2.5 km, loaded or empty. Every truck can also carry four 20-litre jerry cans. The forward post holds 320 litres of diesel, which the officer commanding will release only if the whole round trip can still finish with a 10 per cent fuel reserve in hand. Safety rules forbid transferring fuel between trucks on the move, so each truck must be self-sufficient between the depot and the post. The convoy cruises at 40 km/h and is scheduled to halt 45 minutes at the post to unload. Departure from the depot is at 05:30, and no other halts are planned.
1. Calculate the diesel one truck needs for the complete round trip, and the total for the convoy. Show the consumption rate in litres per kilometre.
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Step 1 - convert the consumption rate. 1 litre per 2.5 km means 1 ÷ 2.5 = 0.4 litres per km.
Step 2 - one leg. 240 km × 0.4 L/km = 96 litres (equivalently 240 ÷ 2.5 = 96).
Step 3 - round trip per truck. 96 × 2 = 192 litres.
Step 4 - convoy total. 192 × 8 trucks = 1 536 litres.
Note that the 10 per cent reserve is not part of this figure; it is a separate requirement checked when deciding whether the post stock is sufficient. A common error is to multiply 96 by 8 and stop there - that gives the one-way figure (768 L), not the round trip.
2. Using the 320 litres held at the forward post, decide whether the round trip can be completed with the required 10 per cent reserve. Support the decision with figures.
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Fuel a truck can carry from the depot: 100 L tank + (4 × 20 L jerry cans) = 180 litres.
Fuel left on arrival at the post: 180 − 96 = 84 litres.
Fuel needed after the post for the return leg plus reserve: 96 L (return) + 19.2 L (10 per cent of the 192 L round trip) = 115.2 litres.
Top-up required at the post per truck: 115.2 − 84 = 31.2 litres.
Convoy requirement: 31.2 × 8 = 249.6 litres.
Decision: 249.6 L is less than the 320 L available, so the round trip is feasible. The post would be left with 320 − 249.6 = 70.4 litres. Each truck would return with the full 19.2 L reserve and no more, which is exactly the ordered minimum - so any delay, detour or extra idling would eat straight into the reserve and the commander should either draw the full 31.2 L per truck or trim the load.
3. State the planned arrival time at the forward post and the time the convoy is back at the depot. What assumption must you state?
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Running time each way: 240 km ÷ 40 km/h = 6 hours.
Arrival at the post: 05:30 + 6 h = 11:30.
Departure from the post: 11:30 + 45 min unloading = 12:15.
Return to depot: 12:15 + 6 h = 18:15.
Assumption stated: the refuelling at the post takes no measurable time, or is done inside the 45-minute halt. If drawing 31.2 L into each of eight trucks adds, say, 15 minutes, the return time becomes 18:30. Always declare this assumption rather than silently ignoring it - examiners mark the stated assumption, and a real convoy order would state it too.