Ch9 Chapter Exercise Answers

Chapter exercise                                                                                                                  p.56

Concept Checking

1.     False

        Friction always (àmay) causes inconvenience.

2.     True

3.     False

        The force of gravity is the same everywhere (different on different celestial bodies).

4.     True

5.     True

   

    Multple Choice

    9.     C

    10.   B

    Short-answer Questions

    13.

           

14.   · The same poles of two magnets repel each other.

        · The opposite poles of two magnets attract each other.

        · A magnet attracts an object made of iron.

        · The pointer of a compass moves under the influence of the Earth’s magnetic field.

        · The force of gravity of the Earth acts on an object.

        (any two or other reasonable answers)

15.   Action and reaction forces do not cancel out each other because they act on different objects.

Skill development (WRITING)                                                                                          p.59

1.     (a)    (i)     starts

                (ii)    stops

                (iii)   direction; speed

        (b)    (i)     starts the motion

                (ii)    stops the motion of the ball

                (iii)   hits the ball; force changes the direction and speed of the ball

2      (a)    (i)     force

                (ii)    centre

        (b)    (i)     a force of gravity

                (ii)    the objects towards the centre of the Moon

        (c)    (i)     a force of gravity on every object around it

                (ii)    pulls the objects towards the centre of Mars