Practise Edexcel A-Level Physics stress-strain graphs and breaking stress through graph areas, fracture energy, safe loads, plastic regions and material choice.
A student carried out an experiment to determine the Young modulus of a sample of stainless steel in the form of a wire. The student added weights to the wire and measured the corresponding extensions.
The wire had an unstretched length of 2.6 m . The diameter of the wire was 5.6×10−4 m.
The student plotted a graph of weight against extension. The graph showed that the limit of proportionality was not exceeded.
The breaking stress for this stainless steel is known to be 480 MPa.
Deduce whether it is safe for the student to increase the weight to 100.0 N.
Use σ = F/A. The maximum safe load is W_max = (480 × 10^6)(2.46 × 10^-7) = 118 N. Since 118 N > 100 N, it is safe.