Calculating Average Kinetic Energy of a Running Boy

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SUMMARY

The discussion focuses on calculating the average kinetic energy of a 60 kg boy running up a slope over 5 seconds. The average velocity is determined to be 1 m/s, derived from the Pythagorean theorem indicating a distance of 5 meters. The average kinetic energy is calculated using the formula KE = 1/2 mv², resulting in 30 Joules. The conversation highlights the importance of understanding average speed in kinetic energy calculations.

PREREQUISITES
  • Understanding of basic physics concepts, specifically kinetic energy.
  • Familiarity with the formula KE = 1/2 mv².
  • Knowledge of average velocity calculations.
  • Application of the Pythagorean theorem in physics problems.
NEXT STEPS
  • Study the relationship between speed and kinetic energy in physics.
  • Learn how to apply the Pythagorean theorem in real-world scenarios.
  • Explore problems involving gravitational potential energy and kinetic energy conversions.
  • Investigate the implications of constant speed assumptions in physics problems.
USEFUL FOR

This discussion is beneficial for physics students, educators, and anyone interested in understanding the principles of kinetic energy and motion analysis.

lingling
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Homework Statement



A boy of 60 kgtakes 5 s to run up the slope in the diagram. (Please refer to the attachment) What is his average kinetic energy?

Homework Equations





The Attempt at a Solution



I don't know the meaning of 'average' kinetic energy. Is this mean kinetic energy per unit time (per second)? How can I calculate it without knowing the velocity of the boy?
 

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His average kinetic energy is the energy corresponding to his average speed
 
How can I know the kinetic energy of the boy without knowing the speed?
My stupid thought was that to use the increase in gravitational potential energy of the boy but I can't get the answer. Why?
 
KE=1/2mv^2

average kintetic energy would come from his average velocity. notice how the distance he went is expressed as a right triangle

WARNING: ANSWER BELOW
try not to look at the answer if you can solve it yourself. i made it white so you must high light it and not see it 'on accident'





[pythagorean theorum tells us the distance he ran was 5 meters and we're given he ran it in 5 seconds, so average velocity is 1 m/s. 1^2 is still 1, and m is 60 so divide it by two and you get 30 N]
 
lingling said:
How can I know the kinetic energy of the boy without knowing the speed?
Assume that he runs up at a constant speed. (Since KE is proportional to speed squared, I think this is an ill-posed problem.)
 

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