Question 8
- (i) State two differences between mass and weight.
Two forces F and 250 N act on a uniform rigid body of weight 50 N as illustrated in the diagram above. Calculate the:
(α) clockwise moment about the pivot;
(β) value of F.
(b) 
The diagram above illustrates the positions P, Q and R of the object moving clockwise in a circular path of centre T. Copy the diagram. Draw straight lines with arrows to indicate the:
(α) net force F at P;
(β) acceleration a at P;
(γ) velocity v at R.
(c) A man weighs 100 N on the surface of the moon. If the acceleration due to gravity on the moon is one – sixth the value on the surface of the earth, calculate the mass of the man on earth. [g = 10 ms-2]
Observation
Part (a) (i) Many candidates answered this question but some however, did not get the maximum score due to inability to pair the answer.
(ii) Candidates performance was below average. Some candidates were confused
about the force that produces either clockwise or anticlockwise. Also, some
candidates either omitted unit or supplied a wrong unit.
Performance was average.
Part (b) (α & β) The question was concise but some candidates did not copy the diagram
and lost some marks. Majority failed because their arrow pointed in the wrong direction.
Performance was below average
Part (c) (i) Performance was low.
The expected answer is:
(a) (i) Differences between mass and weight
Mass |
Weight |
- the amount of matter in an object/body |
- the force of gravity on an object/body |
- scalar |
- vector |
- measured in kg |
- measured in N |
- constant |
- varies from place to place |
(ii)(α) Clockwise moment about the pivot
The moment = 250 x 0.75
= 187.5 Nm
(β) Value of F
Sum of anticlockwise moments = clockwise moment
F x (3 – 0.75) + 50 x (1.5 – 0.75) = 187.5
F = 66.7 N
