WJEC Physics for AS: Study and Rev Guide

Extra questions 1. Express the unit of the spring constant, k , in terms of the base SI units. 2. The unloaded length of a spring is 15.3 cm. When a 500 g mass is suspended from it, its length is 23.7 cm. Calculate the spring constant. 3. Two springs of constant 200 N m –1 and 300 N m –1 at joined end to end. Calculate the strain energy when the springs are put under a tension of 150 N. 4. A rod , X, has a cross-sectional area A . Rod Y has the same length and is made of the same material. Its csa is 2 A . (a) Compare the elastic potential energies if the rods are put under the same tension. (b) Compare the elastic potential energies if X is put under a tension 2 T and Y is put under a tension T . 5. An engineer’s data book gives the following data for copper: Young modulus = 117 GPa; Yield stress = 75 MPa; UTS = 150 MPa; breaking strain = 0.45. A copper wire has diameter 3.25 mm and length 1 km. (a) The wire is subject to a tension which is 90% of the yield stress. Calculate (i) the tension, (ii) the extension and (iii) the strain energy. (b) Sketch the load–extension curve and use it to estimate the work done in stretching it to its breaking point. 6. A student obtained the following results for a piece of copper wire: Diameter of wire, r = 0.272 mm; l 0 = 3.43 m Load / g 50 100 150 200 250 300 350 400 Extension / mm 0.20 0.51 0.78 1.03 1.29 1.50 1.68 1.98 Use these results to determine the Young modulus of the copper. 61 1.5 Solids under stress