Calculating Average Kinetic Energy of a Running Boy

In summary, The boy of 60 kg takes 5 seconds to run up a slope of 5 meters. We are asked to find his average kinetic energy, which is the energy corresponding to his average speed. Since we are given the time and distance, we can use the Pythagorean theorem to calculate his average velocity, which turns out to be 1 m/s. Using the equation KE=1/2mv^2, we can then calculate his average kinetic energy to be 30 N. However, this may be an ill-posed problem since kinetic energy is proportional to speed squared.
  • #1
lingling
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0

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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  • #2
His average kinetic energy is the energy corresponding to his average speed
 
  • #3
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?
 
  • #4
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]
 
  • #5
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.)
 

1. How is kinetic energy calculated?

Kinetic energy is calculated by multiplying the mass of an object by its velocity squared and then dividing by 2. The formula for kinetic energy is KE = (1/2)mv^2, where m is the mass of the object in kilograms and v is the velocity in meters per second.

2. What is the unit of measurement for kinetic energy?

The unit of measurement for kinetic energy is joules (J). This is the same unit used for other forms of energy, such as potential energy and work.

3. Can kinetic energy be negative?

Yes, kinetic energy can be negative. This typically occurs when the velocity and direction of an object are opposite to the direction of motion. In this case, the kinetic energy is considered to be negative because the object is losing energy as it moves.

4. How is kinetic energy related to other forms of energy?

Kinetic energy is one of the two main forms of mechanical energy, the other being potential energy. The total mechanical energy of an object is the sum of its kinetic and potential energy. Kinetic energy can also be converted into other forms of energy, such as thermal energy, through processes like friction.

5. What factors affect the amount of kinetic energy an object has?

The amount of kinetic energy an object has is affected by its mass and velocity. Doubling the mass of an object will double its kinetic energy, while doubling its velocity will quadruple its kinetic energy. The direction of motion and any external forces acting on the object can also affect its kinetic energy.

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