State Hooke's Law.
For forces up to 90 N90\text{ N}90 N, a spring obeys Hooke's Law. A force of 90 N90\text{ N}90 N causes an extension of 60 mm60\text{ mm}60 mm. Calculate the spring constant kkk of the spring in N/m\text{N/m}N/m.
A student makes a spring balance using this spring. The maximum reading of this balance is 110 N110\text{ N}110 N. The student tests his balance with a known weight of 105 N105\text{ N}105 N. He observes that the reading of the balance is not 105 N105\text{ N}105 N. Suggest and explain why the reading is not 105 N105\text{ N}105 N.
245 exam-style questions on CIE IGCSE Physics 1.5 Forces, covering 1.5.1a Forces, resultant force and motion, 1.5.1b Load–extension graphs and the spring constant, 1.5.1c Friction and drag, 1.5.1d Force, mass and acceleration, 1.5.1e Motion in a circular path, 1.5.2a Moment of a force, 1.5.2b Principle of moments and equilibrium, and 1.5.3 Centre of gravity and stability. Each one has a worked solution and a mark scheme showing where the marks go.