Question 1
A rubber cord hangs
from a rigid support. A weight attached to its lower end is gradually
increased from zero,
and then gradually reduced to zero.
The force-extension
curve for contraction is below the force-extension curve for stretching.
What does the shaded
area between the curves represent?
A the
amount of elastic energy stored in the rubber
B the
amount of thermal energy dissipated in the rubber
C the
work done on the rubber cord during stretching
D the work done by the rubber cord during
contraction
Reference: Past Exam Paper – June 2013 Paper 12 Q22
Solution:
Answer:
B.
The area under a
force-extension graph gives us the energy (work).
Work is done on the rubber
cord to stretch it. This is given by the area under the ‘stretching’ curve. In
other words, this area can be considered to be the total energy input.
However, it is observed
that, for rubber, as the weight attached is reduced, the ‘contraction’ curve is
a bit below the ‘stretching curve’. The area under this curve represents the
energy stored in the rubber. That is, it is the useful energy recovered.
It can be seen that this area is lower than the area under the ‘stretching’ curve. This indicates that some energy is lost (it is the amount of thermal energy dissipated in the rubber). This is represented by the shaded area between the 2 curves.
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