Physics Paper 3 WASSCE (SC), 2023

Alternative A

 

Question 1A


(a)

You are provided with a metre rule, two loads, P and Q, a knife edge, K, a set of masses, m and a piece of string.
Use the diagram above as a guide to perform the experiment.

  1. With no loads hanging on the metre rule, balance the metre rule horizontally on the knife edge. Record the position, G, of the knife edge on the balanced metre rule.
  2. Suspend P securely at 15 cm from G, and Q securely at 10 cm from G.The positions of G, P and Q should not be altered throughout the experiment.
  3. Using a mass,  = 40 , balance the metre rule horizontally. Measure and record the distance, y, of m from G.
  4. Evaluate m-1.
  5. Repeat the procedure for m = 50 g, 60 g, 70 g and 80 g. In each case, record the distance, y, and evaluate m-1.
  6. Tabulate the results.
  7. Plot a graph with m-1 as ordinate and y as abscissa.
  8. Determine the slope, s, of the graph.
  9. Determine the value of  given that 15
  10. From the graph, deduce the mass, m, that would produce a balance distance, .
  11. State two precautions taken to ensure good results.

    (b)  (i) State the two conditions necessary for a body to be in equilibrium

     (ii) Two forces 4 N and 3 N act at right angles to each other, calculate the equilibrant of the system of forces.


Observation

 

WEAKNESSES: The candidates mistakenly swapped the axes because they could not tell the difference between the y-axis (ordinate) and the x-axis (abscissa).
STRENGTH: Ability to carry out the instructions and record observations as required.                                                                                 
EXPECTED RESPONSE:

OBSERVATIONS [09]

  • Reasonable value of G correctly determined and recorded to at

   least 1 d.p. in cm.                                                                                          
            (ii)        Five values of m correctly recorded in grams                                              
(Deduct ½ mark for each wrong or missing value)

  • Five values of y correctly determined and recorded to at least 1 d.p.

and in trend.                                                                                                   
Trend: As m increases, y decreases.                                     
(Award 1 mark each)

  • Five values of m-1 correctly evaluated to at least 3 d.p.                              

(Deduct ½ mark for each wrong or missing value)

  • Composite table showing m, m-1 and y.                                             

       GRAPH [06]

  • Axes correctly distinguished (Award ½ mark each)                                                
  • Reasonable scales (Award ½ mark each)                                                      
  • Five points correctly plotted                                                                        

                 (Deduct 1 mark for each wrong or missing point)                            

  • Line of best fit                                                                                                           

     SLOPE (02)

  • Large right-angled triangle                                                                                        

     (ii)     Dm-1 correctly determined                                                                            
(iii)    Dy correctly determined                                                                               
(iv)     correctly evaluated                                                                            

DETERMINATION OF mp [01]

  • Correct substitution                                                                                      
  • Correct calculation                                                                                        

      DEDUCTION OF m [01]

  • Value of m-1 corresponding to y = 27.5 cm correctly shown                       
  • m correctly evaluated                                                                                   

PRECAUTIONS [02]
Award 1 mark each for any 2 reasonable precautions stated in acceptable tense.
E.g.:

  • Avoided draught
  • Avoided parallax error in taking metre rule readings
  • Repeated readings shown on table.

(b)    (i)    Conditions for a body to be in stable equilibrium
                 (α)

  • There should be no net force on the object

OR

  • The sum of forces in one direction must be equal to the sum of forces in the opposite direction.

                 (β)
The sum of the clockwise moments about a point is equal to the sum of the anti-clockwise moment about the same point.
OR
The net torque acting on the body must be zero.

 

II)