Physics Paper 3 WASSCE (SC), 2018

Alternative B

 

Question 1B

 

 

You are provided with a set of masses M, a metre rule, a knife edge and other necessary apparatus.
(i) Balance the metre rule on the knife edge and determine its centre of gravity G
(ii) Suspend the mass M = 50 g at the point A = 5 cm mark of the metre rule and balance the whole arrangement on the knife edge.
(iii) Read and record the balance point K and determine the distance X between A and K.

Observation

 

Part (a) Candidates performance was poor. Many candidates were not able to determine G and K to at least 1 d.p in cm.
Part (b) Candidates response was unsatisfactory.

                        The expected response:

  • The value of G = 50.0 ± 1.0 cm                                                        
  • Six values of M correctly recorded in g                    
  • Six values of K recorded to at least 1dp in cm and in trend                         
  • Six values of X = K - 5 correctly determined                       
  • Six values of  correctly evaluated to at least 3 d.p                          
  • Composite table showing at least M, K, X and 1/X                          
  • Both axes correctly distinguished     
  • Plot a graph using reasonable scales 
  • Draw line of best it
  • Determine the slope and intercept of the graph
  • State any two of the following precautions.

e.g.

  • Avoided errors due to parallax in reading the metre rule
  • Ensured rigid support
  • Avoided draught
  • Repeated readings shown on table
  • Avoided/Noted/Corrected zero error on metre rule
  • Ensured mass did not rest on/touch the table

In part b, the expected answers are:
b(i) Moment of a force about a point is the product of the force and the perpendicular distance of its line of action from the point                                       

(ii)  Moment of couple = one force x perpendicular distance between the forces  .
= 20 x 0.5 = 10 Nm