Conservation of Energy Physics Example 1

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Example 1

medium
A 2 kg2 \text{ kg} ball is dropped from 20 m20 \text{ m}. What is its speed just before hitting the ground? Use g=10 m/s2g = 10 \text{ m/s}^2.

Solution

  1. 1
    At the top: PE=mgh=2×10×20=400 JPE = mgh = 2 \times 10 \times 20 = 400 \text{ J}, KE=0KE = 0.
  2. 2
    At the bottom: all PE converts to KE. 12mv2=400\frac{1}{2}mv^2 = 400
  3. 3
    v=2×4002=400=20 m/sv = \sqrt{\frac{2 \times 400}{2}} = \sqrt{400} = 20 \text{ m/s}

Answer

v=20 m/sv = 20 \text{ m/s}
Conservation of energy states that total mechanical energy is constant in the absence of non-conservative forces. PE at the top equals KE at the bottom.

About Conservation of Energy

A fundamental law of physics stating that the total energy of an isolated system remains constant over time — energy can be transferred between objects.

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