Year 7 Science · Unit 3 · Lesson 11
Challenge Worksheet
Learning Goals
What if…?
Scenario
In 2023, the Australian Road Research Board published data showing that vehicle speed is a key factor in both the likelihood and severity of crashes. Currently, most Australian highways and freeways have a maximum speed limit of 110 km/h. A road safety researcher proposes that reducing all highway speed limits to 90 km/h would lead to a dramatic reduction in fatal crashes. She argues that the reduction in kinetic energy at the new limit would mean cars have a much shorter stopping distance and that any collisions would be less severe.
Using your knowledge of the relationship between speed and kinetic energy, evaluate the researcher's proposal. Calculate the approximate change in KE when speed drops from 110 km/h to 90 km/h (use the pattern: KE is proportional to speed squared). Predict the likely effect on road fatalities and consider any limitations or trade-offs of this policy.
Hint: Compare (90)² with (110)². Relative KE at 110 km/h = 110² = 12 100. Relative KE at 90 km/h = 90² = 8 100. What fraction is this?
1. A news headline reads: "Cutting highway speeds from 110 to 90 km/h only reduces KE by 18% — barely worth the inconvenience." Do you agree or disagree with this claim? Use your calculation above and the science of kinetic energy in your response. (Hint: is 18% fewer fatal crashes "barely worth it"?)
2. Road safety researchers often say "speed kills — but it's kinetic energy that does the damage." Explain what they mean. In your answer, describe what happens to a car's kinetic energy in a crash, and why higher KE causes more severe injury.
Wrap Up
In one sentence, what was the main idea of this lesson?