A physics class is carrying out an experiment to determine the mass of a metal block using a spring and a tilted metre rule.
The student first calibrates the spring: (i) The length of the spring without any load is measured as l0=3.0 cml_0 = 3.0\text{ cm}l0=3.0 cm. (ii) With a load of 100 g100\text{ g}100 g suspended from it, the stretched length is l1=8.0 cml_1 = 8.0\text{ cm}l1=8.0 cm. (iii) Calculate the extension e1e_1e1 of the spring using the equation e1=l1−l0e_1 = l_1 - l_0e1=l1−l0. (iv) Determine the spring constant kkk using the equation k=me1k = \frac{m}{e_1}k=e1m, where m=100 gm = 100\text{ g}m=100 g, and state its unit.
The apparatus is then set up such that the metre rule is resting on a bench at its zero mark (pivot) and is supported at the other end by the spring. The rule is at a small angle to the bench. With only the rule in place, the student measures the length of the stretched spring as l2=4.5 cml_2 = 4.5\text{ cm}l2=4.5 cm. (i) The student then places a metal block with its centre at the 40.0 cm40.0\text{ cm}40.0 cm mark on the metre rule. Explain briefly how the student can ensure that the block is in the correct position. (ii) With the block in position, the student measures the new stretched length of the spring as l3=8.1 cml_3 = 8.1\text{ cm}l3=8.1 cm. Determine the change in extension e2e_2e2 due to the block using the equation e2=l3−l2e_2 = l_3 - l_2e2=l3−l2. (iii) Calculate the mass MMM of the block using the equation M=k(e20.40)M = k \left(\frac{e_2}{0.40}\right)M=k(0.40e2).
Suggest two practical causes of inaccuracy in this experiment.
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.