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Turning effect of forces
6 Class 9 Physics questions with answers and explanations.
Printable worksheet with answer key
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The turning effect of a force about a point is called:
- 1 Torque
- 2 Power
- 3 Pressure
- 4 Momentum
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Correct answer: Torque
Torque, or moment of force, measures the turning effect of a force.
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A force of 10 N acts at a perpendicular distance of 0.5 m from a pivot. What is the torque?
- 1 10.5 N m
- 2 5 N m
- 3 20 N m
- 4 0.05 N m
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Correct answer: 5 N m
Torque = force x perpendicular distance = 10 x 0.5 = 5 N m.
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For a body to be in equilibrium, the resultant force and resultant torque must be:
- 1 Infinite
- 2 Equal to the weight
- 3 Zero
- 4 Maximum
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Correct answer: Zero
Both the net force and the net torque must be zero for equilibrium.
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The centre of gravity of a uniform metre rule lies at the:
- 1 25 cm mark
- 2 0 cm mark
- 3 50 cm mark
- 4 100 cm mark
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Correct answer: 50 cm mark
For a uniform rod the centre of gravity is at its middle, the 50 cm mark.
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Two equal and opposite parallel forces that do not act along the same line form a:
- 1 Lever
- 2 Moment arm
- 3 Couple
- 4 Resultant
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Correct answer: Couple
Such a pair of forces is called a couple and produces rotation without translation.
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A body is more stable when its centre of gravity is:
- 1 Lower and its base wide
- 2 Higher and its base narrow
- 3 Outside the body
- 4 At the top
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Correct answer: Lower and its base wide
A low centre of gravity and a wide base make it harder to topple.