Question 1A
An object of mass M is hung on a spring balance. the position x of the balance is read and the weight w1 of the object in air is determined.
The object is then gradually immersed into water contained in a beaker as illustrated in the diagram above. The pointer position y of the balance is read and the weight w2 of the object in water is determined.
The whole procedure is repeated for five other values of M. In each case, the corresponding values of w1, w2 and w3 are determined from the corresponding positions x, y, and z on the balance.
Fig. 1(a), (b) and (c) show the pointer positions xi, yi and zi for the masses Mi in air, water and the liquid marked L respectively where I = 1, 2, 3, 4, 5 and 6 respectively.
- Measure and record the poiter positions x, y and z.
- Determine the corresponding values of w1, w2 and w3 using the given scale.
- In each case, evaluate u = (w1 – w2) and v = (w1 – w3).
- Tabulate your readings.
- Plot a graph with v on the vertical axis and u on the horizontal axis.
- Determine the slope, s, of the graph.
- What physical quantity does the slope, s, of the graph represent?
- State two precautions that are necessary to ensure accurate results when performing this experiment
(b) (i) Define relative density of a liquid
(ii) A solid has a volume of 30 cm3 and density 2.4 gcm-3. If this solid is suspended on a spring balance with half its volume immersed in water, what would be the reading on the spring balance?
Observation
Part (a) Candidates performance was good. However, many candidates could not measure correctly x, y and z to at least 1 d.p in cm; multiply x, y, and z by
2.0 x 10-2 N; wrongly approximate u and v to 1 s.f. thereby making plotting the values difficult. Also, candidates could not interpret the slope as relative density of liquid L due to lack of theoretical knowledge about the experiment.
Part (b) The question was poorly attempted due to candidates’ lack of understanding of the concept of upthrust thereby having difficulty in solving the problem.
The expected response is as stated below:
- Six values of x, y and z correctly measured to at least 1 d.p and within tolerance of ± 0.1 cm
- Six values of w1, w2, w3 correctly evaluated
- Six values of u = (w1 – w2) and v = (w1 – w3) correctly evaluated
- Show composite table with x, y, z, w1, w2, w3, u and v
- Both axes correctly distinguished
- Plot a graph using reasonable scales
- draw line of best it
- determine the slope of the graph
- state any two of the following precautions.
e.g.
- Avoided parallax error in reading spring balance
- Noted/corrected zero error on spring balance
- Avoided splashing of water/liquid
- Wipe mass M dry before dipping in liquid L
- Repeated readings stated
- Ensured mass does not rest on/touch the beaker
In part b, the expected answers are:
b(i) Relative density of liquid is the ratio of the weight of the liquid/substance to the weight of equal volume of water.
OR
