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Explain why It is easier to knock down a boy who is standing on one foot than one who is standing on two.
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Explain when we carry weight, on one hand, we bend on the other side.
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What is the weight of a body placed at the centre of the earth?
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State two conditions when the work done by a force acting on a body is zero.
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What do you mean by static equilibrium? Give one example.
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One end of a spring is kept fixed while the other end is stretched by a force as shown in the diagram.

(i) Copy the diagram and mark on it the direction of the restoring force.
(ii) Name one instrument which works on the above principle.
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A boy of mass 30 kg is fitting at a distance of 2 m from the middle of a see-saw. Where should a boy of mass 40 kg sit so as to balance the see-saw?
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A ball is placed on a compressed spring. When the spring is released, the ball is observed to fly away.
(i) What form of energy does the compressed spring possess?
(ii) Why does the ball fly away?
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Give an experiment to verify the principle of moments.
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In the atmosphere which colour of light gets scattered the least?
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A metallic blade is made to vibrate at its one end by keeping its other end clamped. The vibrations of the blade die away after some time. Explain, how you lower the frequency of the vibration of the blade?
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Draw a displacement time graph to illustrate damped vibrations.
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Compare the penetrating powers of α, β and γ-radiations.
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Compare the ionising powers of α, β and γ radiations.
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What are α-and β-radiations?
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The figure shows a radioactive source S placed in a thick-walled lead container. The radiations given off pass through a magnetic field acting in direction perpendicular to the plane of paper inwards as shown by X. Copy the diagram and show the path of radiations. Explain why the source is kept in a thick-walled lead container.
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