Math Problem Statement

(L4) A graph of the net force F exerted on an object as a function of x-position is shown for the object of mass M as it travels a horizontal distance 3d. What expression represents the change in the kinetic energy of the object? The graph has a slope of zero from 0 to D, a slope of d/F from d to 2d and again a slope of zero from 2d to 3d.

Solution

To determine the change in the kinetic energy of the object, we use the work-energy theorem, which states:

ΔK=W=F(x)dx\Delta K = W = \int F(x) \, dx

The change in kinetic energy (ΔK\Delta K) is equal to the work done on the object by the net force, which can be calculated as the area under the F(x)F(x) vs. xx-position graph.

Analyzing the graph:

  1. From x=0x = 0 to x=dx = d:

    • The force F(x)F(x) is constant (slope of zero).
    • Let the force be F0F_0.
    • Work done in this region is: W1=F0dW_1 = F_0 \cdot d
  2. From x=dx = d to x=2dx = 2d:

    • The force F(x)F(x) decreases linearly from F0F_0 to 0.
    • This forms a triangular area under the curve.
    • The work done is the area of the triangle: W2=12baseheight=12dF0=F0d2W_2 = \frac{1}{2} \cdot \text{base} \cdot \text{height} = \frac{1}{2} \cdot d \cdot F_0 = \frac{F_0 d}{2}
  3. From x=2dx = 2d to x=3dx = 3d:

    • The force F(x)=0F(x) = 0 (slope is zero).
    • No work is done in this region: W3=0W_3 = 0

Total Work Done:

Wtotal=W1+W2+W3=F0d+F0d2+0W_{\text{total}} = W_1 + W_2 + W_3 = F_0 d + \frac{F_0 d}{2} + 0 Wtotal=32F0dW_{\text{total}} = \frac{3}{2} F_0 d

Expression for the change in kinetic energy:

ΔK=32F0d\Delta K = \frac{3}{2} F_0 d

Would you like further clarifications or additional examples?


5 Related Questions:

  1. What is the significance of the work-energy theorem in physics?
  2. How is work calculated when the force varies with position?
  3. How would the result change if F(x)F(x) decreased non-linearly in the region dx2dd \leq x \leq 2d?
  4. How can we determine the velocity of the object from the kinetic energy?
  5. What happens to kinetic energy if the total work done is negative?

Tip:

When analyzing force-position graphs, always focus on the area under the curve to compute the work done.

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Math Problem Analysis

Mathematical Concepts

Work-Energy Theorem
Force-Position Graph Analysis
Kinetic Energy

Formulas

Work-Energy Theorem: ΔK = W = ∫F(x) dx
Work as area under F(x) graph: W = Area under curve
Work for constant force: W = F × d
Work for triangular force distribution: W = (1/2) × base × height

Theorems

Work-Energy Theorem

Suitable Grade Level

Grades 10-12