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JAMB Physics 1991 Question 11

Question 11

Elasticity

The spiral spring of a spring balance is 25.0 cm long when 5 N hangs on it and 30.0 cm long, when the weight is 10 N. What is the length of the spring if the weight is 3 N assuming Hooke's Law is obeyed?

  1. A.15.0 cm
  2. B.17.0 cm
  3. C.20.0 cm
  4. D.23.0 cm
Show the answer and explanation

Answer: D (23.0 cm)

Explanation

The extra 5 N adds 5 cm, so the spring stretches 1 cm per newton and its natural length is 25 − 5 = 20 cm. With 3 N it is 23 cm.