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Kinetic energy calculation

  • Thread starter lingling
  • Start date
22
0
1. 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?

2. Homework Equations



3. 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?
 

Attachments

Hootenanny

Staff Emeritus
Science Advisor
Gold Member
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His average kinetic energy is the energy corresponding to his average speed
 
22
0
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?
 
533
0
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]
 

Doc Al

Mentor
44,814
1,076
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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