Question 8
- Define:
- terminal velocity
- linear momentum
The diagram above illustrates the trajectory of a projected object. Neglecting friction, how does the
- Horizontal component ux of the initial velocity u change at the points A, B, C?
- vertical component uy of the initial velocity u change at the A, B, C?
- 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.
- Draw and label a diagram of the arrangement
- 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
