AlgebraMediumMass from a spring's linear extension
Algebra practice question
A spring is 12 centimetres long with nothing hung on it, and it stretches 2.5 centimetres for every 100 grams hung from it. What mass, in grams, makes the spring 20 centimetres long?
Answer: 320
The spring must stretch 8 cm. At 2.5 cm per 100 g, that is 8 ÷ 2.5 = 3.2 hundreds of grams, or 320 g.
Common wrong answers
- If you answered 32
- 32 forgets the factor of 100.
- If you answered 200
- 200 comes from 8 ÷ 4, misreading the rate.
- If you answered 800
- 800 comes from 20 ÷ 2.5 × 100, using the whole length instead of the stretch.
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