Register to reply

Finding Potential Energy of a Swing When the Ropes Are Horizontal?

by falconpunch
Tags: energy, horizontal, potential, ropes, swing
Share this thread:
Apr14-12, 12:29 PM
P: 1
1. The problem statement, all variables and given/known data

A 45.0 kg child is in a swing that is attached
to ropes 1.90 m long.
The acceleration of gravity is 9.81 m/s2 .
Find the gravitational potential energy as-
sociated with the child relative to the child’s
lowest position under the following condi-
a) when the ropes are horizontal.
Answer in units of J.

2. Relevant equations

Height of a pendulum:

Potential Energy


3. The attempt at a solution

So first I found the height of the swing at a horizontal position which I assumed is as at 90.


Then I used that height and put it into the formula for potential energy


1213.99 J? = (45)(9.81)(2.75)

but the online homework interface I have to use to input my answer tells me this isn't correct. I was wondering if maybe my answer isn't in Joules, do I need to convert something. Any help would be greatly appreciated.

I realized my problem, i had my calculator in radian's sorry for the stupid question, I'd delete the question if i can find out how
Phys.Org News Partner Science news on
Security CTO to detail Android Fake ID flaw at Black Hat
Huge waves measured for first time in Arctic Ocean
Mysterious molecules in space
Apr15-12, 08:25 AM
HW Helper
P: 6,205
The ropes are 1.9 m long while the height you used is 2.75 m. How exactly did you get 2.75 m using h = L(1-cosθ)?

Register to reply

Related Discussions
Dynamics: max horizontal swing of a pendulum Engineering, Comp Sci, & Technology Homework 4
Finding Potential Energy Introductory Physics Homework 1
Finding an angle of a rope swing involving Energy Introductory Physics Homework 6
Finding the mass of an object suspended by two ropes Introductory Physics Homework 1
Finding x when Elastic Potential Energy equals Kinetic Energy Introductory Physics Homework 3