Why Does Calculating Train Engine Power Result in Different Values?

In summary, the conversation discusses a math problem involving finding the maximum power of a train engine traveling at a given speed and facing a certain resistance. The correct answer is determined to be 1.5 Mega Watts, but the answer book suggests 1.47 Mega Watts. The discrepancy is attributed to a possible error in the original question or calculation.
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Hi. I'm new and am trying to solve a simple question 'Find the max power of a train engine traveling level at 50 metres per second if total resistance to motion is 30 KiloNewtons.

I get power = force times velocity so 30000 x 50 = 1500000 = 1.5 Mega Watts. My answer book says 1.47 Mega Watts. I can see how 1.5MW minus 30KW = 1500000 - 30000 = 1.47MW. Also I can see that power times gravity of 9.8 = 1.5 MW times 9.8 N gives the same answer.

I can't see how you should subtract the force from the sum of the force and the distance, or how vertical gravity can reduce the speed of a horizontally moving train. Thanks :)
 
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  • #2
Your math seems fine. Subtracting 30KW doesn't make sense since 30KW hasn't been computed anywhere, making it a random number. Subtracting the force doesn't make sense since force and power are different units and cannot be added. And yes, gravity plays no role since the problem says 'level'. Also 1.5MW * 9.8 m/sec² results in 14.7 mega-something, not 1.47 mega-something.

I cannot explain the book answer.
 
  • #3
I think these book/web errors often arise when someone modifies the question and fails to check the answer given elsewhere.
That 9.8 produces the right leading digits is suggestive. The original might have been something like "a train of mass 30,000 kg and rolling resistance (or "rolling friction" or whatever) of 0.1..."
 
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Thanks guys, massively appreciated :)
Interesting insight haruspex..
 

FAQ: Why Does Calculating Train Engine Power Result in Different Values?

1. How do I calculate the power of a train engine?

To calculate the power of a train engine, you will need to know the force and velocity of the train. The formula for power is P = F x V, where P is power, F is force, and V is velocity. You can find the force by multiplying the mass of the train by its acceleration. Velocity can be calculated by dividing the distance traveled by the time it took to travel that distance. Once you have the values for force and velocity, you can plug them into the formula to find the power of the train engine.

2. What units should I use for the calculations?

The units you use for the calculations will depend on the units of the given values. It is important to make sure all units are consistent, so if the mass is given in kilograms, the acceleration should be in meters per second squared, and the distance should be in meters. If the values are given in different units, you will need to convert them before plugging them into the formula.

3. Can I use this formula for any type of train engine?

Yes, the formula for calculating power can be used for any type of train engine as long as you have the necessary values. However, keep in mind that this formula only calculates the power of the engine, not taking into account other factors such as friction or air resistance.

4. Is there a simpler way to calculate the power of a train engine?

There are other methods for calculating the power of a train engine, such as using dynamometers or measuring the fuel consumption. However, using the formula P = F x V is the most common and straightforward method.

5. How can I use this information in real life situations?

Knowing the power of a train engine can be useful for engineers and operators to determine the efficiency and performance of the train. It can also be used to compare different train engines and make decisions on which ones to use for certain routes or tasks. Additionally, understanding the power of a train engine can help with troubleshooting and maintenance.

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