Alternative B
Question 1B
You are provided with two knife edges of equal height, a set of masses, a short piece of string with a loop at each end, a metre rule and a half-metre rule.
Carry out the following instructions using the diagram above as a guide.
- Slide the loop of strings onto the metre rule and place it symmetrically on the two knife edges, P and Q, as shown in Fig. 1a.
Do not change the positions of P and Q throughout the experiment.
- Measure and record the height, Y, of C above the surface of the bench as shown in Fig.1a.
- Use the loop of string to hang a mass, m = 50 g at C. Measure the new height, y, as shown in Fig. 1b.
- Evaluate the depression, d = ( Y – y ) of C.
- Evaluate log d and log m.
- Repeat the procedure for four other masses, m = 100 g, 150 g, 200 g and 250 g.
In each case, measure y and evaluate d = ( Y – y ), log d and log m.
- Tabulate the results.
- Plot a graph with log d as ordinate and log m as abscissa.
- Determine the slope, s, of the graph.
- Given a mass, , use the graph to determine the value of y.
- State two precautions taken to ensure good results.
(b) (i) Define the term elasticity.
(ii) A piece of wood 1.5 m long has a cross-sectional area of with one end of the wood fixed to a wall. Calculate the force required to produce a depression of
[Young’s modulus of wood = ]
Observation
WEAKNESSES: Most candidates could not determine the value of from the graph when mass
STRENGTH: Most candidates successfully carried out the given instructions.
EXPECTED RESPONSE:
(a) OBSERVATIONS [09]
- Value of Y correctly recorded to at least 1 d.p in cm.
- Five values of m correctly recorded in grams.
(Deduct ½ mark for each wrong or missing value)
- Five values of y correctly recorded to at least 1 d.p in cm and in trend
Trend: As m increases, y decreases.
(Deduct 1 mark for each wrong or missing value)
- Five values of d = (Y- y) correctly evaluated.
(Deduct ½ mark for each wrong or missing value)
- Five values of log d correctly evaluated to at least 3 d.p.
(Deduct ½ mark for each wrong or missing value)
(vi) Five values of log m correctly evaluated to at least 3 d.p.
(Deduct ½ mark for each wrong or missing value)
- Composite table showing m, y, d, log d and log m.
GRAPH [06]
(i) Both axes correctly distinguished (Award ½ mark each)
(ii) Reasonable Scales (Award ½ mark each)
(iii) Five points correctly plotted
(Deduct 1 mark for each wrong or missing point)
(iv) Line of best fit
SLOPE [02]
(i) Large right-angled triangle
(ii) Dlog d correctly determined
(iii) Dlog m correctly determined
(iv) correctly evaluated
DEDUCTION [02]
log 170 = 2.230
log d corresponding to log 170 correctly shown on graph
d correctly evaluated
correctly evaluated.
PRECAUTIONS [02]
Award 1 mark each for any two correct precautions stated in acceptable tense.
Eg:
- Shielded apparatus from wind/ switched off fans/avoided draught.
- Avoided parallax error in taking readings on metre rule.
- Avoided/noted zero error on metre rule/half-metre rule
- Repeated readings shown on table.
- Ensured the mass did not touch/rest on the table.
- Suspended mass should be stable before taking readings
(b) (i) Elasticity
is the ability of a deformed body to return to its original shape and size when the force causing the deformation is no longer present or removed.
(ii)
