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Check yourself Answers

1Yes, because the weight of the block is less on the moon.

2The minimum force needed to move the block is 3.0 N so the block will not move. The frictional force is then 2.2 N.

3It stays the same. The buoyant force equals the weight of the ice cube and also the weight of the displaced water. So when the ice cube melts, its volume will be that of the displaced water.

4The net force is zero so the resistive force is equal to F.

5C, because the net force has to be opposite to the velocity.

6The same; the acceleration is independent of mass.

7The acceleration of each block is g. The net force on the bottom block is mg − T = ma, so T = 0 since a = g.

8The centripetal acceleration is a c=4 π 2 r T 2=4 π 2×1.5×10 11(365×24×60×60)2≈6×10−3 m s−2, and so the force is F=M a=6×10 24×6×10−3=3.6×10 22 N.

9No, the bob moves in a circular arc and so has centripetal acceleration toward the centre of the arc. Hence the tension force is greater than the weight.