# Kinetic energy calculation

#### lingling

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

• 33.6 KB Views: 309
Related Introductory Physics Homework Help News on Phys.org

#### Hootenanny

Staff Emeritus
Gold Member
His average kinetic energy is the energy corresponding to his average speed

#### lingling

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?

#### Ki Man

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

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
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.)