While steaming at 18.9 knots, your vessel consumes 386 barrels of fuel oil per day. In order to reduce consumption to 251 barrels of fuel oil per day, what is the maximum speed the vessel can turn for?
• Fuel consumption vs. speed is often assumed to vary with the cube of the speed for exam problems • Set up a proportion between (speed)^3 and fuel consumption • Be careful with unit consistency: barrels per day and knots are already compatible in rate form
• If fuel consumption is proportional to the cube of speed, how can you express this as an equation relating the two operating conditions? • Once you have the proportionality equation, how do you solve for the new speed given the new fuel consumption? • After finding the new speed, which answer choice is closest to your computed value?
• Write out the relationship: (Speed₁³ / Speed₂³) = (Consumption₁ / Consumption₂) before solving • Double-check your calculator steps when taking the cube root • Compare your result carefully to the answer choices and watch for rounding differences
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