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ICSE-IX-Physics

03: Laws of Motion

with Solutions -

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  • #
    Section : A
  • Qstn #1
    Explain giving two examples each of :
    (a) Contact forces
    (b) Non - contact forces
    Ans : (a) The forces which act on bodies when they are in physical contact are called contact forces.
    Example: frictional force and force exerted on two bodies during collision.
    (b) The forces experienced by bodies even without being physically touched are called non-contact forces.
    Example: Gravitational force and Electrostatic force.
  • Qstn #2
    Classify the following amongst contact and non - contact forces:
    (a) Frictional force
    (b) Normal reaction force
    (c) Force of tension in a string
    (d) Gravitational force
    (d) Electrostatic force
    (d) Magnetic force
    Ans : Contact force:
    (a) frictional force
    (b) normal reaction force
    (c) force of tension in a string
    Non-contact force:
    (d) gravitational force
    (d) electric force
    (d) magnetic force
  • Qstn #3
    Give one example in each case where :
    (a) The force is of contact, and
    (b) Force is at a distance
    Ans : (a) Force exerted on two bodies during collision.
    (b) Magnetic force between magnetic poles.
  • Qstn #4
    (a) A ball is hanging by string from the ceiling of the roof. Draw a neat labelled diagram showing the forces acting on the ball and the string.
    (b) A spring is compressed against a rigid wall. Draw a neat and labeled diagram showing the forces acting on the spring.
    (c) A wooden block is placed on a table top. Name the forces acting on the block and draw a neat and labelled diagram to show the point of application and direction of these forces.
    Ans : (a)

    (b)
    (c) The forces acting on the block are its weight in the downward direction and the normal reaction force due to the table on the upward direction.
  • Qstn #5
    State one factor on which the magnitude of a non-contact force depends. How does it depend on the factor stated by you?
    Ans :
    • The magnitude of non-contact force on two bodies depends on the distance of separation between them.
    • The force decreases as the distance of separation increases.
    • The force is inversely proportional to the square of the distance of separation.
  • Qstn #6
    The separation between two masses is reduced to half. How is the magnitude of gravitational force between them affected?
    Ans : The magnitude of gravitational force between two masses will become four times as gravitational force varies inversely as the square of distance of separation.
  • Qstn #7
    State the effects of a force applied on
    A non-rigid, and
    A rigid body.
    How does the effect of the force differ in the two cases?
    Ans : A force when applied on a non-rigid body changes the inter-spacing between its constituent particles and therefore causes a change in its dimensions and can also produce motion in it.
    On the other hand, a force when applied on a rigid body, does not change the inter-spacing between its constituent particles and therefore it does not change the dimensions of the body but causes motion in it
  • Qstn #8
    Give one example in each of the following cases where a force:
    (a) Stops a moving body.
    (b) Moves a stationary body.
    (c) Changes the size of a body.
    (d) Changes the shape of a body.
    Ans : (a) A fielder on the ground stops a moving ball by applying a force with his hands.
    (b) The pull exerted by horse makes a cart moves.
    (c) In a cycle pump, when the piston is lowered, the air is compressed to occupy a less volume.
    (d) On pressing a piece of rubber, its shape changes.
  • #
    Section : A-s1
    Multiple Choice type: 3(A)
  • Qstn #1
    Which of the following is a contact force:
    (a) Electrostatic force
    (b) Gravitational force
    (c) Frictional force
    (d) Magnetic force
    Ans : Frictional force is a contact force.
  • Qstn #2
    The non - contact force is :
    (a) Force of reaction
    (b) Force due to gravity
    (c) Tension in string
    (d) Force of friction
    Ans : Force due to gravity is a non-contact force.
  • #
    Section : B
  • Qstn #1
    Name the physical quantity that causes motion in a body.
    Ans : Force causes motion in a body
  • Qstn #2
    Is force needed to keep a moving body in motion?
    Ans : Force is not needed to keep a moving body in motion.
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