Hint
Choose and retain a positive direction; distinguish signed quantities from magnitudes. Balance horizontal forces because the velocity is constant.
Worked solution
(a)
Balance horizontal forces because the velocity is constant.
Zero horizontal resultant requires drive=9 N.
Answer: \(9\) N
(b)
Balance the upward support against the weight.
Zero vertical acceleration gives \(\displaystyle R=Mg=80 N\).
Answer: \(80\) N
(c)
Convert the given mass to weight using the stated g.
The gravitational force is \(\displaystyle Mg=80 N\) downward.
Answer: \(80\) N
Maths4U indicative marking guidance
Maths4U indicative marking guidance, not an official mark scheme. Credit complete valid alternative methods and consequential reasoning. An unexplained result does not earn a method mark.
(a) · 2 marks
- 1 mark: Balance horizontal forces because the velocity is constant.
- 1 mark: Give the correct requested result, retaining signs, units and any domain restrictions.
Alternative methods: Any complete mathematically valid alternative method with the same restrictions and equivalent exact result is acceptable.
Common error: Constant velocity is compatible with several nonzero balanced forces.
(b) · 2 marks
- 1 mark: Balance the upward support against the weight.
- 1 mark: Give the correct requested result, retaining signs, units and any domain restrictions.
Alternative methods: Any complete mathematically valid alternative method with the same restrictions and equivalent exact result is acceptable.
Common error: Do not confuse zero acceleration with zero speed.
(c) · 2 marks
- 1 mark: Convert the given mass to weight using the stated g.
- 1 mark: Give the correct requested result, retaining signs, units and any domain restrictions.
Alternative methods: Any complete mathematically valid alternative method with the same restrictions and equivalent exact result is acceptable.
Common error: Constant velocity is compatible with several nonzero balanced forces.
Total: 6 marks.