Question 3
An elastic wire extends by 1.0 cm when a mass of 20 g hangs from it. Calculate the additional mass that would be required to cause a further extension of 2.0 cm.
This was not a popular question among the candidates. Majority of the candidates who attempted this question performed poorly because they failed to use proportion method which is simpler than other methods.
Observation
The expected answer is:
Calculation of additional mass needed to cause the required extension
F = ke or k = Let additional mass = M
= = 20 N m-1 Additional extension by M = 0.02 m
Let M = additional mass OR F = ke
k = 20 = Force due to 20 g mass: 0.02 x 10 =k (0.01)
0.06 = 0.02 + M Force due to M: M x10 = k(0.02)
M = 0.04 kg or 40 g M = 0.04 kg or 40 g
M = 0.04 kg or 40 g