Practice question

If you reduce your speed by half before crashing, how does this affect kinetic energy?

  1. It remains the same
  2. It is reduced by two times
  3. It is reduced by three times
  4. It is reduced by four times

Answer: A — It remains the same

Kinetic energy is calculated using the formula \( KE = \frac{1}{2} mv^2 \), where \( m \) is the mass of the object and \( v \) is its velocity. This formula shows that kinetic energy is directly related to the square of the velocity. If you reduce your speed by half, you would replace \( v \) in the equation with \( \frac{v}{2} \). When applying this in the kinetic energy formula, you get: \( KE_{new} = \frac{1}{2} m \left(\frac{v}{2}\right)^2 \) When you simplify this, it turns into: \( KE_{new} = \frac{1}{2} m \left(\frac{v^2}{4}\right) = \frac{1}{4} \cdot \frac{1}{2} mv^2 \) This indicates that the new kinetic energy is one-fourth of the original kinetic energy. Thus, by reducing speed by half, the kinetic energy is significantly reduced—specifically, to a quarter of what it was before the reduction in speed. Consequently, the correct response reflects this decrease in kinetic energy when speed is

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