Question 15
A spring of unextended length 0.50 m is stretched by a force of 2.0 N to a new length of 0.90 m.
The variation of its length with tension is as shown.
How much strain energy is stored in the spring?
A 0.40 J B 0.80 J C 0.90 J D 1.8 J
Reference: Past Exam Paper – June 2007 Paper 1 Q19
Solution:
Answer: A.
When the tension is 0 N (no force is applied), the length of the spring is 0.50 m. This is the original length of the spring.
A tension of 2.0 N causes the spring to extend, from its original length, by (0.9 – 0.5) m.
Strain energy = Area under tension-length graph
We need to consider the area of the triangle formed.
Strain energy = ½ × (2.0 – 0) × (0.9 – 0.5) = 0.40 J
Note that strain (= extension / original length) is NOT the same as strain energy.
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