4.08a& 4.08b The KE and GPE Challenge


Purpose: To apply the concepts of kinetic energy and gravitational potential energy to selected problems

Introduction: You will now apply your knowledge of the concepts of kinetic energy and gravitational potential energy in solving some selected problems. Be sure to review the previous tutorial as you complete your work.

Materials: scientific calculator

Procedure:

  1. Carefully read the problems given below. Prepare solutions using the techniques you have learned in previous activities.

  2. Before you submit your solutions, be sure to check each one using the rubric shown below.


Rubric:

Criteria Point Value
"Givens" are correctly listed. Proper symbols are used for the variables. Constants are included if necessary for the solution. 1 Point
The proper equation is shown. 1 Point
All work to obtain the solution is shown. Numerical substitution for the symbols in the equation is shown. 1 Point
The correct numerical answer is shown. 1 Point
The correct unit (label) is shown with the numerical answer. 1 Point

Problems:
  1. Here is the URL for the Washington Monument. Go to the web site to retrieve the information for part A.

    1. If 1 meter = 3.28 feet, what is the height of the Washington Monument in meters?

    2. A worker assigned to the restoration of the Washington Monument is checking the condition of the stone at the very top of the monument. A nickel with a mass of 0.005 kg is in her shirt pocket. What is the gravitational potential energy (GPE) of the nickel at the top of the monument?

    3. What is the kinetic energy (KE) of the nickel in her shirt pocket at the top of the monument?

    4. If the nickel accidentally falls out of her pocket, what will happen to the gravitational potential energy (GPE) of the nickel as it falls to the ground?

    5. If the nickel accidentally falls out of her pocket, what will happen to the kinetic energy (KE) of the nickel as it falls to the ground?

 
  1. Consider the concepts of kinetic energy (KE) and gravitational potential energy (GPE) as you complete these questions. A ball is held 1.4 meters above the floor. Use the terms KE of GPE as your answers.

    1. When the ball is held motionless above the floor, the ball possesses only ? energy.

    2. If the ball is dropped, its ? energy decreases as it falls.

    3. If the ball is dropped, its ? energy increases as it falls.

    4. In fact, in the absence of air resistance, the amount of ? energy when the ball is held motionless above the floor equals the amount of ? energy at impact with the floor.

 
  1. We will now use energy considerations to find the speed of a falling object at impact. Artiom is on the roof replacing some shingles when his 0.55 kg hammer slips out of his hands. The hammer falls 3.67 m to the ground. Neglecting air resistance, the total mechanical energy of the system will remain the same. The kinetic energy and the gravitational potential energy possessed by the hammer 3.67 m above the ground is equal to the kinetic energy and the gravitational potential energy of the falling hammer as it falls. Upon impact, all of the energy is in a kinetic form. The following equation can be used to represent the relationship:

    GPE + KE (top) = GPE + KE (at impact)

    Because the hammer is dropped from rest, the KE at the top is equal to zero.
    Because the hammer is at base level, the height of the hammer is equal to zero; therefore the PE upon impact is zero.


    We may write our equation like this:
    GPE (top) = KE (at impact)
    This gives us the equation:
    (
    mgh) (top) = 1/2 mv2 (at impact)

    1. Notice that the mass of the hammer "m" is shown on both sides of the equation. According to the math rules we have learned, what does this mean?

    2. Manipulate the equation (rearrange the variables) to solve for v. (Remember that manipulating an equation does not involve numbers and substitutions. You just rearrange the equation. v = ?)

    3. Use your equation from part B to find the speed with which the hammer struck the ground.

 
  1. Eight million (8,000,000) kg of water are at the verge of dropping over Niagara Falls to the rocks 50.0 meters below. What is the change in gravitational potential energy as the water splashes on the rocks below?
Niagara Falls picture

Joule's Jungle

4.08 Energizer - The KE and GPE Challenge

  1. 4.08a: Submit your completed work in the assessment section.

  2. 4.08b Oral Component: Please contact your instructor for your oral evaluation.

  3. Be sure to save your work as an .rtf file. Include both the questions and the appropriate answers.


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