Online Test Banks
Score higher
See Online Test Banks
eLearning
Learning anything is easy
Browse Online Courses
Mobile Apps
Learning on the go
Explore Mobile Apps
Dummies Store
Shop for books and more
Start Shopping

How to Convert Potential Energy into Kinetic Energy

When an object falls, its gravitational potential energy is changed to kinetic energy. You can use this relationship to calculate the speed of the object’s descent. Gravitational potential energy for a mass m at height h near the surface of the Earth is mgh more than the potential energy would be at height 0. (It’s up to you where you choose height 0.)

For example, say that you lift a 40-kilogram cannonball onto a shelf 3.0 meters from the floor, and the ball rolls and slips off, headed toward your toes. If you know the potential energy involved, you can figure out how fast the ball will be going when it reaches the tips of your shoes. Resting on the shelf, the cannonball has this much potential energy with respect to the floor:

image0.png

The cannonball has 1,200 joules of potential energy stored by virtue of its position in a gravitational field. What happens when it drops, just before it touches your toes? That potential energy is converted into kinetic energy. So how fast will the cannonball be going at toe impact? Because its potential energy is converted into kinetic energy, you can write the problem as the following:

image1.png

Plugging in the numbers and putting velocity on one side, you get the speed:

image2.png

The velocity of 7.7 meters/second converts to about 25 feet/second. You have a 40-kilogram cannonball — or about 88 pounds — dropping onto your toes at 25 feet/second. You play around with the numbers and decide you don’t like the results. Prudently, you turn off your calculator and move your feet out of the way.

  • Add a Comment
  • Print
  • Share
blog comments powered by Disqus
Advertisement

Inside Dummies.com

Dummies.com Sweepstakes

Win $500. Easy.