Grade 10 general science – Turning effect of force Quiz
1. What is the turning effect of a force about a pivot commonly called?
The turning effect of a force about a pivot is called a moment or torque; friction, mass and pressure are different physical quantities.
2. What is the SI unit of moment (turning effect)?
Moment is force × perpendicular distance, so its unit is N·m (newton metre). Joule and N/m are different units; newton is unit of force.
3. Which action will increase the turning effect of a force on a wrench used to loosen a bolt?
Moment = force × perpendicular distance, so increasing the distance from the pivot increases the turning effect.
4. On a seesaw (teeter-totter), when the left person pushes down producing rotation counterclockwise, that rotation is called:
Rotation in the opposite direction to clockwise is called anticlockwise; seesaw rotation is described as clockwise or anticlockwise moment.
5. A seesaw is balanced. Which condition must be true about the moments about the pivot?
For rotational equilibrium about a pivot, clockwise and anticlockwise moments must be equal so there is no net rotation.
6. A force of 50 N is applied at a perpendicular distance of 2.0 m from a pivot. What is the moment about the pivot?
Moment = force × perpendicular distance = 50 N × 2.0 m = 100 N·m.
7. If the distance from the pivot is halved while the applied force stays the same, what happens to the moment?
Moment is directly proportional to the perpendicular distance; halving the distance halves the moment.
8. Why is it easier to open a door by pushing at the handle rather than near the hinge?
A larger perpendicular distance from the pivot (hinge) increases the moment for the same force, making it easier to open.
9. A wheelbarrow is an example of which class of lever?
In a wheelbarrow the load is between the fulcrum (wheel) and the effort (handles), which defines a second-class lever.
10. Which statement describes a first-class lever?
A first-class lever has the fulcrum between effort and load (example: a seesaw).
11. A 60 N weight hangs 0.5 m from a pivot. To balance it, an effort is applied at 1.5 m on the other side. What effort is needed?
Balance requires moments equal: effort × 1.5 m = 60 N × 0.5 m → effort = (60×0.5)/1.5 = 20 N.
12. What is the centre of gravity of an object?
The centre of gravity is the single point where the whole weight of an object can be considered to act.
13. For an object to be in rotational equilibrium about a pivot, the sum of the clockwise moments must be:
Rotational equilibrium requires clockwise and anticlockwise moments to balance so there is no net rotation.
14. A force of 30 N acts at 0.20 m from a pivot at an angle of 60° to the lever. What is the moment about the pivot? (Use sin 60° = 0.866)
Perpendicular component = 30 N × sin60 = 25.98 N; moment = 25.98 N × 0.20 m ≈ 5.2 N·m.
15. Why does a longer spanner (wrench) make turning a stuck nut easier?
Longer lever arm increases moment (force × distance), giving greater turning effect for the same applied force.
16. A uniform metre rule is balanced at the 45.0 cm mark when a 2.0 N mass is hung at 20.0 cm. What is the weight of the metre rule? (Take centre at 50.0 cm)
Take moments about 45.0 cm: weight × (50−45)=W×0.05 m must balance 2 N × (45−20)=2×0.25=0.50 N·m. So W = 0.50/0.05 = 10 N.
17. What is a couple in turning effect terms?
A couple consists of two equal opposite parallel forces separated by a distance; their combined effect is a pure turning moment.
18. Two students sit on a seesaw. Student A has mass 30 kg and sits 1.0 m from the pivot. Student B has mass 50 kg. How far from the pivot must student B sit to balance the seesaw? (Take g constant so weights proportional to mass.)
Balance: 30 kg × 1.0 m = 50 kg × d → d = 30/50 = 0.60 m.
19. How can the mechanical advantage of a lever be increased?
Mechanical advantage improves if the effort arm is made longer compared with the load arm, reducing the effort needed.
20. Which direction of applied force gives the greatest turning effect for a given lever arm?
Perpendicular force gives the full magnitude of force as the perpendicular component; any angled force has a smaller perpendicular component.
21. Two equal forces of 10 N act as a couple separated by 0.20 m. What is the moment of the couple?
Moment of a couple = force × separation = 10 N × 0.20 m = 2.0 N·m.
22. Which change will reduce the force needed to lift a heavy load using a crowbar acting as a lever?
Increasing the effort arm gives a larger moment for the same force, so less force is required to lift the load.
23. A 5 N force is applied at 0.40 m from a pivot at an angle of 30° to the lever. What is the moment about the pivot? (Use sin 30° = 0.5)
Perpendicular component = 5 N × sin30° = 2.5 N; moment = 2.5 N × 0.40 m = 1.0 N·m.
24. For a uniform rod of length L pivoted at one end, where does the weight act when calculating the turning effect?
The centre of gravity of a uniform rod is at its midpoint, so its weight acts at L/2 from the end.
25. If a force produces a clockwise moment of 15 N·m and another force produces an anticlockwise moment of 9 N·m about the same pivot, what is the net moment and the rotation tendency?
Net moment = 15 N·m clockwise − 9 N·m anticlockwise = 6 N·m clockwise, so rotation tendency is clockwise.
26. A force of 12 N is applied at the end of a 0.25 m rod perpendicular to it. What moment does it produce?
Moment = force × distance = 12 N × 0.25 m = 3.0 N·m.
27. Which of the following best describes why tools like wheelbarrows and pulleys are useful in everyday life in Kenya?
Simple machines increase mechanical advantage (turning effect) making it easier to move or lift heavy loads with less effort.