Power to Horsepower Conversion: Multiply or Divide?

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SUMMARY

The discussion centers on converting power measured in watts to horsepower, specifically addressing the confusion between multiplying and dividing by the conversion factor. The correct method is to divide the power in watts by 745.7 W to obtain horsepower, as demonstrated with a power value of 638.79 W resulting in approximately 0.856286 hp. Participants emphasize the importance of unit cancellation in calculations and suggest estimating results before using a calculator to validate the outcome.

PREREQUISITES
  • Understanding of basic physics concepts, particularly power and units of measurement.
  • Familiarity with the conversion factor between watts and horsepower (1 hp = 745.7 W).
  • Basic arithmetic skills for performing multiplication and division.
  • Knowledge of dimensional analysis to ensure unit consistency in calculations.
NEXT STEPS
  • Research the principles of dimensional analysis in physics.
  • Learn more about power calculations in mechanical systems.
  • Explore the differences between various units of power, including metric and imperial systems.
  • Investigate practical applications of horsepower in engineering and automotive contexts.
USEFUL FOR

This discussion is beneficial for students in physics or engineering, educators teaching unit conversions, and anyone interested in understanding power measurements in practical applications.

anonymous820
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Homework Statement



how do u get from power to horsepower?
mass=60 kg
weight=588.6 N
height=7 m
time=6.45 s
power= 638.79 W

Homework Equations



----

The Attempt at a Solution



multiply by 746 W to get: 476537.34 hp
or divide by 746 W to get: .856286 hp

i think its divide rather than multiply b/c then the watts cancel and ure left with hp, but I am not sure. that's my only question. multiply or divide?
 
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1 horsepower = 745.7 watts
or 1 W = 1/745.7 Hp, so you replace the 'W' with (1/745.7)Hp.

Or just think would 638W be more or less than 1 hp and roughly how many would it be?
It's always worth estimating the answer before putting the numbers in a calculator.
 
Last edited:
less. so IT IS divide. thanks. i knew 400,000 hp was unreasonable for a person. this was a lab btw.
 
Last edited:
anonymous820 said:
i think its divide rather than multiply b/c then the watts cancel and ure left with hp, but I am not sure. that's my only question. multiply or divide?

You have the correct instinct that you should be able to carry your units along in your calculation to help you keep the numbers in the right places. Here's a thread that should help your insight -- check out my post #10 and the subsequent comments:

https://www.physicsforums.com/showthread.php?t=130989

Very important trick to use and master in your math and physics and engineering studies!
 

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