Physics Paper 3, Nov/Dec 2012

Questions:	1	2	3	Main

General Comments
Weakness/Remedies
Strength

Question 1
Question 1 A test tube is weighed and its mass, m0 = 20 g is recorded. It is then loaded with sufficient lead shots so that it floats vertically in a beaker of water as illustrated in the diagram above. The depth, d, of immersion of the test tube and content is measured and recorded. The test tube and content are taken out of the water, weighed and the mass, ms read and recorded. The mass, me of the lead shot is determined and recorded. The quantity L = me is then evaluated and recorded. D The test tube and its content are returned into the water. The test tube is slightly depressed vertically in the water and released so that it performs vertical oscillations. The time, t, for 10 complete oscillations is noted and recorded. The procedure is repeated four other values of me Fig 1 (a) shows the masses msi, of the test tube and its contents, fig. 1 (b) shows the corresponding depth di of immersion and fig. 1(c) shows the corresponding time ti for 10 complete vertical oscillations of the test tube in water, where i = 1, 2, 3, 4 and 5. Read and record the masses msi of the loaded test tube. Measure and record the depth di of immersion. Read and record the corresponding time ti, for 10 complete oscillations. Evaluate, in each case, the mass me of the lead shots and the period T of oscillation. Also evaluate Ti2 and Li = mei di Tabulate your readings Determine the mean value Q of Li Plot a graph with me on the vertical axis and T2 on the horizontal axis. Determine the slope, s, of the graph and the intercept, c, on the vertical axis Evaluate k = 4π2s (Take π = 22/7) Q State two precautions that are necessary to ensure accurate results when performing this experiment. (b) (i) List the forces acting on the loaded test-tube as it perform vertical oscillation in the water. (ii) Explain why the amplitude of oscillation of the loaded test-tube decreases with time.
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Observation
This questions was popular among the candidates and its was fairly well attempted. However, some candidates that attempted this question were unable to determine me, Q mean, T and T2. Some recorded their values to wrong number of decimal places. Few candidates calculated T as n/t instead of t/n. Some candidates also experiences difficulty in presenting a complete and composite table for the data. This led to poor plotting of the resulting graphs and stating of acceptable precautions. Part (b) of this question was poorly rendered as few of the candidates recalled correctly the three forces acting on the test-tube in the water while majority mentioned only two of the forces. Many of the candidates also failed to recognize fluid friction (viscosity) as the force responsible for the gradual decrease in the amplitude of oscillation of the loaded test-tube with time in water. The expected answers are: Candidates are expected to read and record five values of the following variables and quantities to the required number of decimal places and tolerance: Ms , d, me , t , T, T2 and L Read and record Qmean Plot five points on graph using reasonable scales on correctly distinguish axes. Draw line of best fit Determine the slope of the graph using large right-angled triangle Determination of the intercept c on the vertical axis Evaluation of k = 4π2s/Q State any two of the following precautions e.g - Avoided parallax error in reading clock / weighing balance / metre rule - Zero error noted and corrected on metre rule / clock/weighing balance - Repeated readings stated - Dry/clean test tube before weighing - Avoid draught or wind The expected answers to part (b) are: Weight, upthrust and viscous force / drag or liquid friction. The amplitude of oscillation of a loaded test tube decreases with time because of the viscous drag (force) which opposes the motion OR Because of damping effect due to viscous drag (liquid friction)This questions was popular among the candidates and its was fairly well attempted. However, some candidates that attempted this question were unable to determine me, Q mean, T and T2. Some recorded their values to wrong number of decimal places. Few candidates calculated T as n/t instead of t/n. Some candidates also experiences difficulty in presenting a complete and composite table for the data. This led to poor plotting of the resulting graphs and stating of acceptable precautions. Part (b) of this question was poorly rendered as few of the candidates recalled correctly the three forces acting on the test-tube in the water while majority mentioned only two of the forces. Many of the candidates also failed to recognize fluid friction (viscosity) as the force responsible for the gradual decrease in the amplitude of oscillation of the loaded test-tube with time in water. The expected answers are: Candidates are expected to read and record five values of the following variables and quantities to the required number of decimal places and tolerance: Ms , d, me , t , T, T2 and L Read and record Qmean Plot five points on graph using reasonable scales on correctly distinguish axes. Draw line of best fit Determine the slope of the graph using large right-angled triangle Determination of the intercept c on the vertical axis Evaluation of k = 4π2s/Q State any two of the following precautions e.g - Avoided parallax error in reading clock / weighing balance / metre rule - Zero error noted and corrected on metre rule / clock/weighing balance - Repeated readings stated - Dry/clean test tube before weighing - Avoid draught or wind The expected answers to part (b) are: Weight, upthrust and viscous force / drag or liquid friction. The amplitude of oscillation of a loaded test tube decreases with time because of the viscous drag (force) which opposes the motion OR Because of damping effect due to viscous drag (liquid friction)