Physics (Essay) Paper 2 WASSCE (PC), 2016

Question 8

 

 

  1. Define:
    1. terminal velocity
    2. linear momentum

 

The diagram above illustrates the trajectory of a projected object. Neglecting friction, how does the

  1. Horizontal component ux of the initial velocity u change at the points A, B, C?
  2. vertical component uy of the initial velocity u change at the A, B, C?

 

  1. A uniform bar XY of mass 5.0 kg and length 300 cm is suspended by two inextensible identical wires P and Q. P is attached 50 cm from the end X and Q to the centre of mass C of the bar, such that they are vertical. A mass of 10.0 kg is attached to the end X of the bar.
  2. Draw and label a diagram of the arrangement
  3. Determine the distance from the centre of mass C where another mass of 10.0 kg should be hung on the bar to keep the bar horizontal and to make the tension in Q four times the tension in P. [g = 10 ms-2]

Observation

 

 

Part (a) (i) Many candidates answered this question. Majority of the candidates failed                     because they could not technically express themselves. The following                                      terms/expression were expected: fluid, free fall, equilibrium of forces or zero                    resultant force.
            (ii) Some candidates defined it as “the product of mass and velocity” and did not                   score any mark because they failed to feature linear in the definition.
           
                  Performance is low.
Part (b) A few candidates scored the full mark in this question. This may be due to lack of sound knowledge of the trajectory.

Performance was low.

Part (c) (i) Many candidates either drew or did not draw the right diagram for the question because incorrect indication of P, Q, distances as well as 10 kg load.
(ii) The numerical was poorly labelled

Performance was low.

The expected answer is:

8. (a) (i) Terminal Velocity

The speed with which an object moves (vertically) downward in a fluid when the resultant force acting on it is zero.                                                                                              

(ii)      Linear Momentum                                                       
The product of the mass and velocity of an object moving along a straight path                                                                                                                                           
(b) At Point A
ux = constant                                                                                                 
uy = decreases                                                                                               

     At Point B
ux = constant 

uy = zero 

                                                                                                                 

    At Point C
ux = constant 

uy = increases