(a) Many candidates rendered linear momentum wrongly. Majority defined 'momentum' instead of
'linear momentum' .
(b) Majority of the responding candidates were able to state the required number of instances where
Newton's third law of motion is applicable.
(c) Several candidates failed to apply the formula adequately. Many candidates substituted 2ms·'
since in the question they were told the ball rebounced after impact.
(d) Responses was fairly satisfactory.
The expected answers are:
(a)(i) Linear momentum of a body moving in a straight line is the product
of its mass and its velocity.
Accept product of mass and linear velocity.
Any valid additional information
e.g.
- Its unit is kgms" - Do not accept Ns
- it is a vector quantity.
(ii) Impulse of a force is the product of the (large) force acting on a body and the (short)
time during which it acts. Any valid additional information e.g.
Any valid additional information
e.g.
- Its unit is Ns - Do not accept kgms"
- it is a vector quantity.
(b) Instances where Newton's third law of motion is applicable
- recoil of a gun
- jet propulsion/rocket propulsion
- action of sprinkler/lawn spray
- Accept any other valid instance(s)
(c) Impulse = Ft = m(v- u)
= 4[2-(-3)]
= 20Ns
(d) Weight, W=mg
= (5000 + 4000) x 10
= 90,000N.
Downward action = upward reaction
90,000 = 50(v-0)
v = 90,000
50
= 1.8 X 103 ms-1.
