Work and Potential Energy Problem

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SUMMARY

The forum discussion centers on a physics problem involving a 140 Watt motor with 70% efficiency used to lift a load 5 meters in 5 seconds. The user calculates the motor's output power as 98 Watts and determines the potential energy (PE) to be 490 Joules. By applying the formula PE = mgH, the user concludes that the load mass is 10 kilograms. However, the expected answer is 110 kilograms, prompting the user to seek clarification on the discrepancy.

PREREQUISITES
  • Understanding of basic physics concepts such as work, energy, and power.
  • Familiarity with the formula for potential energy (PE = mgh).
  • Knowledge of motor efficiency calculations.
  • Ability to perform unit conversions and basic algebra.
NEXT STEPS
  • Review the concept of motor efficiency and its impact on output power.
  • Learn about gravitational potential energy calculations in physics.
  • Study the relationship between work, energy, and power in mechanical systems.
  • Explore common mistakes in physics problem-solving and how to avoid them.
USEFUL FOR

This discussion is beneficial for physics students, educators, and anyone interested in understanding the principles of work and energy in mechanical systems.

bengaltiger14
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Homework Statement



A 140 Watt motor (70% efficient) is available to raise a load 5 meters into the air. If the task takes 5 seconds to complete, how heavy was the load in kilograms?


I first determine the motot output: 140W * 70% == 98 Watts

I then multiply 98 Watts by 5 seconds to get PE = 490Joules

Now, setting 490Joules = mgH and solving for m, I get 10 kilograms

The answer is supposed to be 110kg according to my professor but I cannot get to that number. What am I doing wrong?

Thanks
 
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Your answer looks good to me. I don't think you did anything wrong. (Ask your professor to show her solution.)
 

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