2 Quck Questions on Work and Energy

[bigpapasmurf]

Homework Statement

1. If a 0.2 kg ball is dropped from a height of 8 m, what is its kinetic energy when it hits the ground?


2. Jane, looking for Tarzan, is running at top speed (4.6 m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward?

Homework Equations

Kinetic Energy = (1/2) mass*gravity*height
Potential Energy= mass*gravity*height
not sure if this equation is right... distance=(1/2)(gravity)(time^2)
Velocity= (change in distance)/time

The Attempt at a Solution

my work got deleted for both the question (error in webassign) and now I have no idea how I got the answers. (both wrong) But they were 9.5J for the first one and 14.2m for the second question.

 

[berkeman]

Homework Equations

Kinetic Energy = (1/2) mass*gravity*height
Potential Energy= mass*gravity*height
not sure if this equation is right... distance=(1/2)(gravity)(time^2)
Velocity= (change in distance)/time

Your KE equation is wrong. It's mixed up with the correct PE equation. Fix the KE equation, and you should get the correct answers.

 

[bigpapasmurf]

woops I had it actually I just wrote typed it out wrong it is (1/2)mv^2

 

[NBAJam100]

woops I had it actually I just wrote typed it out wrong it is (1/2)mv^2

For part a, maybe I am missing something, but did you say that your answer of 9.5J was correct? because I am thinking otherwise unless I am missing something very obvious.

E(i)=E(f) ---> PE=KE in this case correct?