Hooke's law and force-extension graphsEdexcel A-Level Physics: Mind map

Exam questions on Hooke's law and force-extension graphs

1. A helical spring obeys Hooke's law. A tensile force of 4.0 N extends it by 25 mm.
   The spring is instead compressed by 15 mm. Calculate the force needed, assuming Hooke's law is obeyed in compression.2 marks
2. A metal wire is loaded in steps and the extension is measured. The graph of force against extension is a straight line through the origin up to a force of 12 N, where the extension is 1.5 mm. Beyond 12 N the line curves so that its gradient decreases. When the wire is unloaded from a force of 12 N it returns to its original length. When it is unloaded from a force of 14 N it is found to be 0.30 mm longer than at the start.
   Explain what the 0.30 mm permanent extension shows about the wire.2 marks
3. A car suspension spring has a stiffness of 4.5 × 10⁴ N m⁻¹. When the car is parked, the spring supports one quarter of the car's mass of 1200 kg. The spring obeys Hooke's law up to a compression of 0.18 m. Take g = 9.81 N kg⁻¹.
   Calculate the compression of the spring when the car is parked.3 marks