Calculating Total Energy of a High Diver's Leap

[lbella026]

Homework Statement

A high diver, mass 50kg sits atop the diving platform with 10,000 Joules of stored gravitational potential energy (PE). The platform has a height of 20m. The diver makes his leap. When the diver has dropped 3/4 of the height what is diver total energy (KE + PE).

Homework Equations

KE=(1/2)mass x speed squared

The Attempt at a Solution

I don't know how to find the Kinetic energy using the equation without knowing the speed.

 

[pgardn]

Homework Statement

A high diver, mass 50kg sits atop the diving platform with 10,000 Joules of stored gravitational potential energy (PE). The platform has a height of 20m. The diver makes his leap. When the diver has dropped 3/4 of the height what is diver total energy (KE + PE).

Homework Equations

KE=(1/2)mass x speed squared

The Attempt at a Solution

I don't know how to find the Kinetic energy using the equation without knowing the speed.

Have you "guys" done any conservation of Energy problems?

 

[lbella026]

We haven't yet. I'm unsure of what equation to use which would apply. That equation and the W=force x distance are the only ones I can find in the book. Is there another equation I could use? thanks!

 

[pgardn]

We haven't yet. I'm unsure of what equation to use which would apply. That equation and the W=force x distance are the only ones I can find in the book. Is there another equation I could use? thanks!

So you have not talked about Potential Energy, or gravitational potential energy in class? Along with F x d = Work and Kinetic energy?

 

[lbella026]

ohhh would the potential energy be the same as the kinetic energy?? KE =10,000 J. would the potenial energy be lost and kinetic energy gainned?

 

[pgardn]

ohhh would the potential energy be the same as the kinetic energy?? KE =10,000 J. would the potenial energy be lost and kinetic energy gainned?

The diver has the same amount of Mechanical energy (PE + KE) or (U + K) all the way through his dive. His mechanical energy is conserved.

So if the diver is not moving he has all his energy in the form of potential energy. If the diver is moving and he is above the lowest point in his path he has potential energy and kinetic energy (yes some potential energy is now kinetic energy). And at the lowest point in the path he is moving his fastest, all his potential energy is now kinetic energy. But at every position the total energy is the same.

 

[lbella026]

ok now I understand. Thank you so much!