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Calculate the length of arm of couple, if a force of 13 N produces a moment of couple of 14.3 Nm.
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On a see-saw, two children of masses 30 kg and 50 kg are sitting on one side of it at distance 2 m and 2.5 m respectively, from its middle, where should a man of mass 74 kg sit to balance it?
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What is the nature of the lines of force of the magnetic field due to a straight current carrying wire?
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In the diagram XY is a straight conductor carrying current in the direction marked by the arrow. The conductor is held vertical by passing it through a horizontal cardboard sheet.

Draw three magnetic lines of force on the board and mark the direction of magnetic field in your diagram. State two factors on which magnitude of magnetic field at a point, depends.
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State two differences between light and sound waves.
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Describe a set up for plotting the magnetic lines of force in: (i) A straight wire, (ii) A circular coil and (iii) A straight solenoid.
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Clockwise moment produced by a force about a fulcrum is considered to be ______.
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When a ray of light travels normal to the given surface, then the angle of refraction is ______.
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The diagram shows wheel O pivoted at point A. Three equal forces F1, F2 and F3 act at point B on the wheel.

- Which force will produce maximum moment about A?
- Give a reason for your answer in (a).
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What should be the angle between the direction of force and the direction of displacement, for work to be negative?
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Which electrical component protects the electric circuit in case of excess current and which can also be used as a switch?
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Name the wire to which this electrical component is connected in an electric circuit.
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A door lock is opened by turning the lever (handle) of length 0.2 m. If the moment of force produced is 1 Nm, then the minimum force required is ______.
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A force 'F' moves a load from A to C as shown in the figure below. For the calculation of the work done, which of these lengths would you use as the displacement?

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If live wire makes an accidental contact with the metal case, which circuit (A or B) in the diagram, illustrating an electric iron, is considered safe for the user (Assuming the fuse is present in the live wire in both circuits)? Justify your answer.

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A metal rod AB of length 80 cm is balanced at 45 cm from the end A with 100 gf weights suspended from the two ends.
- If this rod is cut at the center, C, then compare the weight of AC to the weight of BC. (Use >, < or =)
- Give a reason for your answer in (a).
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A person standing in front of a cliff fires a gun and hears its echo after 3 s. If the speed of sound in air is 336 ms−1.
- Calculate the distance of the person from the cliff.
- After moving a certain distance from the cliff, he fires the gun again, and this time the echo is heard 1.5 s later than the first. Calculate the distance that the person moved.
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A nut is opened by a wrench of length 25 cm. If the least force required is 10 N, find the moment of force needed to turn the nut.
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The diagram in Fig shows two forces F1 = 5 N and F2 = 3 N acting at points A and B respectively of a rod pivoted at a point O, such that OA = 2 m and OB = 4 m.

Calculate:
- the moment of force F1 about O.
- the moment of force F2 about O.
- total moment of the two forces about O.
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A body, when acted upon by a force of 20 kgf, gets displaced by 1 m. Calculate the work done by the force, when the displacement is
- in the direction of force,
- at an angle of 60° with the force, and
- normal to the force. (g = 10 N kg-1)
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