Physics (AS & A Level) · May / June 2016 · Paper 21 · Question 4

the energy (stored) in a body due to its extension/compression/deformation/ change in shape/size [1]

two values of F/x are calculated which are the same e.g. 10.4 / 40 = 0.26 and 6.5 / 25 = 0.26 or ratio of two forces and the ratio of the corresponding two extensions are calculated which are the same e.g. 5.2 / 10.4 = 0.5 and 20 / 40 = 0.5 (B1) or gradient of graph line calculated and coordinates of one point on the line used with straight line equation y = mx + c to show c = 0 (B1) (so) force is proportional to extension (and so Hooke’s law obeyed) [2]

1. k = F / x or k = gradient gradient or values from a single point used e.g. k = 10.4 / (40 × 10–2) k = 26 N m–1 [2]

2. work done = area under graph or ½Fx or ½(F2 + F1)(x2 – x1) or ½kx2 or ½k(x2 2 – x1 2) = ½ × 10.4 × 0.4 – ½ × 5.2 × 0.2 or ½ × (5.2 + 10.4) × 20 × 10–2 or ½ × 26 × (0.42 − 0.22) = 1.6 J [3]

remove the force and the spring goes back to its original length [1]