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NCERT Exemplar · Class 9 Science Motion

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Multiple Choice Questions 1–11 (part 1 of 3)

  1. Exercise 1

    A particle is moving in a circular path of radius r. The displacement after
    half a circle would be:
    (a)
    Zero
    (b)
    π r (c) 2\displaystyle 2 r
    (d)
    2\displaystyle 2π r

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    (c)
    (c) \(\displaystyle 2r\). Half a circle carries the particle to the diametrically opposite point, so the straight-line displacement equals the diameter. \[\text{Displacement} = \text{diameter} = 2r \] NCERT_Solution_Class9_Science_Exemplar_Ch8_Q1

  2. Exercise 2

    A body is thrown vertically upward with velocity u, the greatest height h to
    which it will rise is,
    (a)
    u/g
    (b)
    u2\displaystyle u^{2}/2g
    (c)
    u2\displaystyle u^{2}/g
    (d)
    u/2g

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    (b)
    (b) \(\displaystyle \dfrac{u^{2}}{2g}\). At the greatest height the velocity is momentarily zero. \[v^{2}=u^{2}-2gh \] \[0=u^{2}-2gh \ \Rightarrow\ h=\dfrac{u^{2}}{2g} \]

  3. Exercise 3

    The numerical ratio of displacement to distance for a moving object is
    (a)
    always less than 1\displaystyle 1
    (b)
    always equal to 1\displaystyle 1
    (c)
    always more than 1\displaystyle 1
    (d)
    equal or less than 1\displaystyle 1

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    NCERT’s answer
    (d)
    (d) Equal to or less than 1. Displacement is the straight-line join of the start and end points; distance is the actual path length, so displacement can never exceed distance.

  4. Exercise 4

    If the displacement of an object is proportional to square of time, then the
    object moves with
    (a)
    uniform velocity
    (b)
    uniform acceleration
    (c)
    increasing acceleration
    (d)
    decreasing acceleration

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    (b)
    (b) Uniform acceleration. Displacement \(\displaystyle s\propto t^{2}\) is the signature of motion starting from rest under constant acceleration. \[s=\dfrac{1}{2}at^{2}\quad (u=0)\ \Rightarrow\ s\propto t^{2} \]

  5. Exercise 5

    From the given v - t graph (Fig. 8.1\displaystyle 8.1), it can be inferred that the object is
    (a)
    in uniform motion
    (b)
    at rest
    (c)
    in non-uniform motion
    (d)
    moving with uniform acceleration
    NCERT_Question_Class9_Science_Exemplar_Ch8_Q5

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    (a)
    (a) in uniform motionFig. $\displaystyle 8.1$'s v-t line is horizontal at a fixed, non-zero v, so velocity does not change with time: \[a = \dfrac{\Delta v}{\Delta t} = 0\] same velocity at every instant.Answer: (a) in uniform motion.

  6. Exercise 6

    Suppose a boy is enjoying a ride on a merry-go-round which is moving
    with a constant speed of 10\displaystyle 10 m s−1\displaystyle s^{-1}. It implies that the boy is
    (a)
    at rest
    (b)
    moving with no acceleration
    (c)
    in accelerated motion
    (d)
    moving with uniform velocity

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    (c)
    (c) In accelerated motion. Speed stays constant, but on a circular path the velocity's direction keeps changing, so there is a centripetal acceleration. \[a_c=\dfrac{v^{2}}{r}\neq 0 \] NCERT_Solution_Class9_Science_Exemplar_Ch8_Q6

  7. Exercise 7

    Area under a v - t graph represents a physical quantity which has the unit
    (a)
    m2\displaystyle m^{2}
    (b)
    m (c) m3\displaystyle m^{3}
    (d)
    m s−1\displaystyle s^{-1}

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    NCERT’s answer
    (b)
    (b) \(\displaystyle \text{m}\). Velocity multiplied by time gives a displacement. \[\text{Area}=v\times t = (\text{m s}^{-1})(\text{s}) = \text{m} \] NCERT_Solution_Class9_Science_Exemplar_Ch8_Q7

  8. Exercise 8

    Four cars A, B, C and D are moving on a levelled road. Their distance
    versus time graphs are shown in Fig. 8.2. Choose the correct statement
    (a)
    Car A is faster than car D.
    (b)
    Car B is the slowest.
    (c)
    Car D is faster than car C.
    (d)
    Car C is the slowest.
    NCERT_Question_Class9_Science_Exemplar_Ch8_Q8

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    (b)
    (b) Car B is the slowestSlope of a distance-time graph is speed: \[v = \dfrac{d}{t}\] Fig. $\displaystyle 8.2$'s slopes run \(\displaystyle C > D > A > B\), so \(\displaystyle v_C > v_D > v_A > v_B\) -- B's line is least steep.Answer: (b) Car B is the slowest.

  9. Exercise 9

    Which of the following figures (Fig. 8.3\displaystyle 8.3) represents uniform motion of a moving object correctly? NCERT_Question_Class9_Science_Exemplar_Ch8_Q9

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    NCERT’s answer
    (a)
    (a) Uniform motion has constant velocity, so distance grows directly with time — a straight line through the origin. (b) speeds up (steepening slope), (c) slows down (flattening slope), (d) shows no motion at all (velocity zero).Answer: (a)

  10. Exercise 10

    Slope of a velocity - time graph gives
    (a)
    the distance
    (b)
    the displacement
    (c)
    the acceleration
    (d)
    the speed

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    (c)
    (c) The slope of a velocity-time graph is the change in velocity per unit time — the definition of acceleration. \[\text{slope} = \dfrac{\Delta v}{\Delta t} = a \]Answer: (c) the acceleration

  11. Exercise 11

    In which of the following cases of motions, the distance moved and the
    magnitude of displacement are equal?
    (a)
    If the car is moving on straight road
    (b)
    If the car is moving in circular path
    (c)
    The pendulum is moving to and fro
    (d)
    The earth is revolving around the Sun

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    (a)
    (a) Car on a straight road. Moving along a single straight line without reversing, the path length and the straight-line displacement are the same; the other three paths curve or loop back.