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Physics · Grades 9–12

Change in kinetic energy

Square each speed before subtracting; a loss gives a negative change.

Make a worksheet

Rule and assumptions

Square each speed before subtracting; a loss gives a negative change.

ΔEₖ = ½m(v² − u²)

Worked examples

A 17 kg object changes speed from 12 m/s to 6 m/s. Find final minus initial kinetic energy. Round to 3 decimal places if needed. Answer in J.

ΔEₖ = ½m(v² − u²) 0.5 × 17 × (6² − 12²) = -918

-918 J

A 9 kg object changes speed from 5 m/s to 10 m/s. Find final minus initial kinetic energy. Round to 3 decimal places if needed. Answer in J.

ΔEₖ = ½m(v² − u²) 0.5 × 9 × (10² − 5²) = 337.5

337.5 J

Try two questions

  1. A 10 kg object changes speed from 15 m/s to 16 m/s. Find final minus initial kinetic energy. Round to 3 decimal places if needed. Answer in J.

  2. A 13 kg object changes speed from 2 m/s to 4 m/s. Find final minus initial kinetic energy. Round to 3 decimal places if needed. Answer in J.

Answers and reasoning

Answers and marking notes
  1. 155 J

    ΔEₖ = ½m(v² − u²) 0.5 × 10 × (16² − 15²) = 155

  2. 78 J

    ΔEₖ = ½m(v² − u²) 0.5 × 13 × (4² − 2²) = 78

Further reading and review references

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Learning preview · independent educational and translation review required. Suggested grades are not official curriculum alignment.