Mechanical Energy Physics Example 2

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Example 2

medium
A ball with 68 J68 \text{ J} of mechanical energy is at height 3 m3 \text{ m}. Its mass is 1 kg1 \text{ kg}. What is its speed? Use g=10 m/s2g = 10 \text{ m/s}^2.

Solution

  1. 1
    PE at 3 m3 \text{ m}: mgh=1×10×3=30 Jmgh = 1 \times 10 \times 3 = 30 \text{ J}.
  2. 2
    KE: E−PE=68−30=38 JE - PE = 68 - 30 = 38 \text{ J}.
  3. 3
    Speed: v=2×KEm=761≈8.72 m/sv = \sqrt{\frac{2 \times KE}{m}} = \sqrt{\frac{76}{1}} \approx 8.72 \text{ m/s}

Answer

v≈8.72 m/sv \approx 8.72 \text{ m/s}
Knowing the total mechanical energy and the PE at any height lets us find the KE and speed. This is a direct application of energy conservation.

About Mechanical Energy

The total of kinetic energy and potential energy in a mechanical system at any given moment.

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