Physics I Workbook For Dummies with Online Practice, 3rd Edition
Book image
Explore Book Buy On Amazon

When you have objects in motion, you have kinetic energy. When, for example, you slide an object on a frictionless surface, the work you do goes into the object’s kinetic energy:

W = KEfKEi

If you have an object with mass m moving at speed v, its kinetic energy is

image0.jpg

That’s the energy of motion.

Sample question

  1. Say that you push a spaceship, mass 1,000.0 kg, by applying a force of 1.00 x 104 N for 1.00 m. How fast does the spaceship end up traveling?

    The correct answer is 4.47 m/s.

    1. Find the total work done:

      (1.00 x 104 N)(1.00 m) = 1.00 x 104 J
    2. The work done on the spaceship goes into its kinetic energy, and its initial kinetic energy is 0, so its final kinetic energy is 1.0 x 104 J.

    3. Use the equation for kinetic energy and solve for v:

      image1.jpg

      The final speed is 20.01/2 = 4.47 m/s.

Practice questions

  1. You’re applying 600.0 N of force to a car with a mass of 1,000.0 kg. You’re traveling a distance of 100.0 m on a frictionless, icy road. What is the car’s final speed?

  2. You’re ice skating and traveling at 30.0 m/s. If your mass is 65 kg, what is your kinetic energy?

  3. You’re traveling in a car at 88 m/s. If you have a mass of 80.0 kg and the car has a mass of 1,200.0 kg, what is the total kinetic energy of you and the car combined?

  4. You’re applying 3,000.0 N of force to a hockey puck with a mass of 0.10 kg. It travels over a distance of 0.10 m on a frictionless ice rink. What is the puck’s final speed?

Following are answers to the practice questions:

  1. 11 m/s

    1. Find the total work done:

      (600 N)(100 m) = 6.0 x 104 J

    2. The work done on the car goes into its kinetic energy, so its final kinetic energy is 6.0 x 104 J.

    3. Use the equation for kinetic energy and solve for v:

      image2.jpg
    4. Plug in the numbers:

      image3.jpg

      The final speed = 1201/2 = 11 m/s.

  2. 2.9 x 104 J

    1. The equation for kinetic energy is

      image4.jpg
    2. Plug in the numbers:

      image5.jpg
  3. 4.9 x 106 J

    1. The equation for kinetic energy is

      image6.jpg
    2. Plug in the numbers:

      image7.jpg
  4. 77 m/s

    1. Find the total work done:

      (3,000 N) (0.10 m) = 300 J

    2. The work done on the puck goes into its kinetic energy, so its final kinetic energy is 300 J.

    3. Use the equation for kinetic energy and solve for v:

      image8.jpg
    4. Plug in the numbers:

      image9.jpg

      The final speed = 6,0001/2 = 77 m/s.

About This Article

This article is from the book:

About the book author:

This article can be found in the category: