The SI unit of force is the newton and 3 N with 4 N acting at right angles give a resultant of 5 N, so this Year 12 sheet opens with units and a 3-4-5 resultant. The moment is defined through the perpendicular distance and weight is named as a force.
Key Takeaways
The SI unit of force is the newton (Q1).
3 N and 4 N at right angles give a resultant of 5 N (Q2).
Q4 records weight as a force on the body.
Section A: Multiple Choice Questions (1 Mark Each)
Choose the correct option for each question.
1.The SI unit of force is the...
(a) joule(b) newton(c) watt(d) pascal
2.Two forces of 3 N and 4 N act at right angles on a body. The magnitude of the resultant force is...
(a) 7 N(b) 1 N(c) 5 N(d) 12 N
3.The moment of a force about a point is the product of the force and...
(a) the perpendicular distance from the point to the line of action(b) the mass of the body(c) the speed of the body(d) the time for which the force acts
4.Which quantity is a vector?
(a) mass(b) weight(c) temperature(d) energy
5.Hooke's law states that, for a spring, the extension is proportional to...
(a) the applied force(b) the mass cubed(c) the temperature(d) the spring length
6.The centre of gravity of a body is the point where...
(a) the whole weight of the body appears to act(b) the body is lightest(c) the body has its greatest density(d) the body is in motion
Section B: Short Answer Type Questions (2 Marks Each)
Show all steps clearly.
7.State Hooke's law.
8.Define the moment of a force about a point.
9.State the two conditions for a body to be in equilibrium under the action of coplanar forces.
10.State the principle of moments.
11.Distinguish between mass and weight.
12.Define the centre of gravity of a body.
13.What is meant by a couple?
14.A body is suspended from a single point and hangs at rest. Where does its centre of gravity lie, and why?
Section C: Numericals & Word Problems (3 Marks Each)
Apply the concepts to solve the problems. Show all working.
15.A uniform plank of weight 200 N and length 4 m is pivoted at one end and held horizontal by a vertical force F at the other end. Taking moments about the pivot, calculate F.
16.A spring extends by 5 cm when a force of 20 N is applied. Using Hooke's law F = kx, calculate the spring constant and the extension produced by a force of 50 N.
17.A box of weight 100 N rests on a smooth slope inclined at 30° to the horizontal. Calculate the component of the weight acting down the slope using mg sinθ.
18.Two forces of 6 N and 8 N act at right angles on a body. Calculate the magnitude of their resultant and its direction relative to the 6 N force.
19.A 20 kg mass rests on a slope inclined at 25°. Using the component mg sinθ with g = 9.8 m s⁻², calculate the component of its weight parallel to the slope.
20.A uniform 6 m board is pivoted at its centre. A child of weight 300 N sits 1.5 m from the pivot on one side. Taking moments about the pivot, calculate how far a child of weight 200 N must sit on the other side to balance the board.
Answer Key
1. b) newton
2. c) 5 N
3. a) the perpendicular distance from the point to the line of action
4. b) weight
5. a) the applied force
6. a) the whole weight of the body appears to act
7. Refer to solution guide.
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20. Refer to solution guide.
End of Worksheet
People Also Ask
What is the SI unit of force?
The newton, option (b) in this worksheet (Q1).
What is the resultant of 3 N and 4 N at right angles?
5 N, option (c) in this worksheet (Q2).
What is the moment of a force measured about?
The perpendicular distance from the point to the line of action, option (a) in this worksheet (Q3).
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