Physics Paper 3 WASSCE (SC), 2021

Alternative B

 

Question 1B

 

You are provided with a set of masses, a metre rule, a thread, two retort stands and clamps, a stop watch , a knife edge and spilt corks.

Carry out the following instructions using the diagram above as a guide.

  1. Determine the centre of gravity, C, of the metre rule using knife edge.
  2. Read and record the mass, M, of the metre rule written n the reverse side of it.
  3. Suspend the metre rule by means f two parallel threads of equal length, h = 70cm, with one at the 10 cm mark and the other at the 90 cm mark of the metre rule.
  4. Attach a mass m = 30 g firmly to the metre rule at C. ensure that the graduated face of the metre rule is facing upwards and that d = 80cm throughout the experiment.
  5. Set the metre rule into small angular oscillations about the vertical axis through its centre of gravity by displacing its ends in opposite directions.
  6. Determine the time, t, for 20 oscillations and evaluate the period T, T2 and T-2.
  7. Repeat the procedure for four other values of m = 40 g, 50 g, 60 g and 70 g.
  8. Plot a graph of T-2 on the vertical axis and m on the horizontal axis.
  9. Determine the slope, s, of the graph.
  10. Evaluate Q = .
  11. State two precautions taken to ensure accurate results.

 

(b)        (i)Give two examples of simple harmonic motion other than the motion of a simple pendulum

            (ii)        Explain the term centre of gravity of a body.

 

Observation

 

Part (a) Majority candidates attempted this question. Performance was fair.
Part (b) Candidates response was satisfactory.

The expected response:

1 (a) OBSERVATIONS

  • Value of C correctly measured and recorded to at least 1 d.p and within 50 ± 0.5 cm   
  • Value of M correctly recorded                                                                           
  • Five values of m correctly recorded in g.                                                           
  • Five values of t correctly measured and recorded to at least 1d.p in s and in trend.

Trend: As m increases, t decreases

  • Five values of T correctly evaluated to at least2 d.p.                                        
  • Five values of T 2 correctly evaluated to at least3 d.p                                       
  • Five values of T -2 correctly evaluated to at least 3 d.p                                     
  • Composite table showing at least m, t, T, T 2 and T -2                                        

GRAPH

  • Both axes correctly distinguished                                    
  • Reasonable scales                                                            
  • Five points correctly plotted                                                                               
  • Line of best fit.                                                                                        

SLOPE

  • Large right – angled triangle                                            
  • ∆ T-2 correctly determined                                                                                   
  • ∆ m correctly determined                                                                                    
  • correctly evaluated                                                                                       

EVALUATION OF Q
Q =                                                                                                     
Correct substitution                                                                     
Correct arithmetic                                                                                    

PRECAUTIONS
- Ensured threads were firm /tight.
- Ensured supports of pendulum were rigid.
- Avoided parallax error on metre rule/stopwatch/ clock.
- Zero error was noted and corrected on metre rule/stopwatch/stopclock
. Ensured smooth and regular oscillations in a horizontal plane.
- Repeated readings shown on table.
- Avoided draught.
NB: Avoiding conical oscillation should not be accepted

b(i) Examples of simple harmonic motion other than simple pendulum.

  • A body at the end of a spring performing vertical oscillations with small amplitude
  • A floating rod/loaded test tube suspended in a liquid performing vertical oscillations with small amplitude.
  • A liquid performing oscillations in a U-tube with a small amplitude.
  • Vertical motion of a loaded spiral spring.
  • Motion of a sounded/vibrating tuning fork.
  • A vibrating loaded bar clamped to a bench / A vibrating cantilever.
  • Motion of a see-saw.
  • Motion of steel ball in a curved dish