AS Daily A Level Physics question
A mass is hung from a single vertical spring, causing it to extend and store an amount of elastic potential energy E. Two identical springs are then arranged in parallel and the same mass is hung from the combination. What is the total elastic potential energy now stored in the parallel spring system?
Answer
The correct answer is B.
Correct: B — E/2. Two identical springs in parallel have double the effective spring constant of a single spring. For the same stretching force (the weight of the mass), this stiffer combination will only extend by half the original amount. Since the elastic potential energy stored is proportional to the extension (for a constant force, E = ½ * Force * extension), halving the extension also halves the stored energy. A is incorrect; this would be the case if energy was proportional to extension squared and the change in the effective spring constant was ignored. C is incorrect; this wrongly assumes the energy is unchanged because the weight is unchanged, failing to account for the reduced extension. D is incorrect; this would be the energy stored if the two springs were arranged in series, which would double the extension for the same force.