Rotational and Circular Motion

21 free MDCAT Physics MCQs on Rotational and Circular Motion (PM&DC syllabus), each with the answer, an explanation and the textbook line it comes from. Tap to check, no sign-up.

Tap an answer to check it · 21 questions

1. Question 1

   The fixed line about which rotation takes place is called the:
   • ALine of action
   • BAxis of rotation
   • CRadius vector
   • DPlane of rotation
   Show answer and explanation

   Answer: B) Axis of rotation

   It may be a pivot, hinge or other support. Source: 11 Physics Book FBISE, p. 54.

2. Question 2

   The study of motion along a circular path without reference to forces or torques is:
   • AStatics
   • BRotational dynamics
   • CRotational kinematics
   • DFluid dynamics
   Show answer and explanation

   Answer: C) Rotational kinematics

   It parallels linear kinematics. Source: 11 Physics Book FBISE, p. 54.

3. Question 3

   The property by which a body maintains its state of rest or uniform rotational motion about a fixed axis is its:
   • ATorque
   • BAngular momentum
   • CMoment of inertia
   • DCentripetal force
   Show answer and explanation

   Answer: C) Moment of inertia

   Also called rotational inertia. Source: 11 Physics Book FBISE, p. 64.

4. Question 4

   Gravity produced artificially in a space station to counteract weightlessness is called:
   • AFree fall
   • BZero gravity
   • CMicrogravity
   • DArtificial gravity
   Show answer and explanation

   Answer: D) Artificial gravity

   It is produced by rotating the station about its own axis. Source: 11 Physics Book FBISE, p. 72.

5. Question 5

   One radian is approximately equal to:
   • A57.3
   • B90
   • C3.14
   • D180
   Show answer and explanation

   Answer: A) 57.3

   2 pi rad = 360, so 1 rad = 360/6.28 = 57.3 degrees. Source: 11 Physics Book FBISE, p. 55.

6. Question 6

   The SI unit of angular momentum is:
   • Akg m/s
   • Bkg m2/s
   • Ckg m2/s2
   • DN m
   Show answer and explanation

   Answer: B) kg m2/s

   Dimensions [ML2T-1]; N m is the unit of torque. Source: 11 Physics Book FBISE, p. 65.

7. Question 7

   An 856 kg car moving at 12.0 m/s on a curve needs a centripetal force of 7250 N. The radius of the curve is about:
   • A1.4 m
   • B17 m
   • C120 m
   • D8.5 m
   Show answer and explanation

   Answer: B) 17 m

   r = m v^2 / F = 856 x 144 / 7250 = 17 m. Source: 11 Physics Book FBISE, p. 64.

8. Question 8

   A 3.6 kg uniform disc of radius 0.31 m rotates at 120.4 rad/s. Its angular momentum is about:
   • A2.67 J s
   • B41.66 J s
   • C20.83 J s
   • D120.4 J s
   Show answer and explanation

   Answer: C) 20.83 J s

   L = I omega = (1/2 m R^2) omega = 0.173 x 120.4 = 20.83 J s. Source: 11 Physics Book FBISE, p. 70.

9. Question 9

   A ring-shaped space station of radius 1.5 km gives artificial gravity of 9.8 m/s2. Its period of rotation is about:
   • A9.8 s
   • B0.08 s
   • C12.4 s
   • D77.7 s
   Show answer and explanation

   Answer: D) 77.7 s

   omega = sqrt(g/R) = 0.08 rad/s; T = 2 pi / omega = 77.73 s. Source: 11 Physics Book FBISE, p. 73.

10. Question 10

    An astronaut feels weightless inside the International Space Station because the station is:
    • AOutside Earth's gravity
    • BIn free fall
    • CAt complete rest
    • DBeyond the atmosphere
    Show answer and explanation

    Answer: B) In free fall

    Station and astronaut fall together; gravity there is still about 95% of its surface value. Source: 11 Physics Book FBISE, p. 71.

11. Question 11

    The direction of angular displacement, a vector quantity, is given by the:
    • AHead to tail rule
    • BLeft hand rule
    • CRight hand rule
    • DParallelogram law
    Show answer and explanation

    Answer: C) Right hand rule

    Curl the fingers in the direction of rotation; the thumb gives the direction. Source: 11 Physics Book FBISE, p. 55.

12. Question 12

    When a ball is whirled in a circle on a string, the centripetal force is provided by the:
    • AFriction of the air
    • BWeight of the ball
    • CTension in the string
    • DNormal force
    Show answer and explanation

    Answer: C) Tension in the string

    Greater speed or radius needs greater tension. Source: 11 Physics Book FBISE, p. 62.

13. Question 13

    For a car going around an unbanked curve without skidding, the centripetal force is provided by:
    • AThe car's weight
    • BAir resistance
    • CEngine thrust
    • DStatic friction
    Show answer and explanation

    Answer: D) Static friction

    Banking the road lets the normal force provide it instead. Source: 11 Physics Book FBISE, p. 61.

14. Question 14

    On a frictionless banked curve, the banking angle needed for a given speed and radius is:
    • AIndependent of vehicle mass
    • BProportional to vehicle mass
    • CInversely proportional to mass
    • DZero for heavy vehicles
    Show answer and explanation

    Answer: A) Independent of vehicle mass

    tan theta = v^2/(r g); higher speeds and smaller radii need steeper banking. Source: 11 Physics Book FBISE, p. 62.

15. Question 15

    A centrifuge separates substances suspended in a liquid by:
    • AHeating it strongly
    • BSpinning it very quickly
    • CEvaporating the liquid
    • DCooling it slowly
    Show answer and explanation

    Answer: B) Spinning it very quickly

    Denser particles collect at the bottom of the tube; cream separators work the same way. Source: 11 Physics Book FBISE, p. 63.

16. Question 16

    In rotational motion, moment of inertia plays the role of:
    • AVelocity
    • BForce
    • CMass
    • DMomentum
    Show answer and explanation

    Answer: C) Mass

    A larger moment of inertia is harder to accelerate angularly. Source: 11 Physics Book FBISE, p. 64.

17. Question 17

    Torque is equal to moment of inertia multiplied by:
    • AAngular acceleration
    • BAngular velocity
    • CLinear acceleration
    • DAngular momentum
    Show answer and explanation

    Answer: A) Angular acceleration

    tau = I alpha, the rotational form of F = m a. Source: 11 Physics Book FBISE, p. 71.

18. Question 18

    A spinning ice skater pulls her arms close to her body. Her angular velocity:
    • ADecreases
    • BIncreases
    • CStays the same
    • DBecomes zero
    Show answer and explanation

    Answer: B) Increases

    Moment of inertia decreases, so omega increases to keep I omega constant. Source: 11 Physics Book FBISE, p. 67.

19. Question 19

    A gyroscope maintains its orientation by making use of:
    • ABuoyant force
    • BLinear momentum
    • CCentripetal force
    • DAngular momentum
    Show answer and explanation

    Answer: D) Angular momentum

    Used in aeroplane and navigation systems. Source: 11 Physics Book FBISE, p. 68.

20. Question 20

    A flywheel is a mechanical component that:
    • AStores energy by spinning
    • BReduces friction in bearings
    • CMeasures angular speed
    • DChanges direction of torque
    Show answer and explanation

    Answer: A) Stores energy by spinning

    It smooths power delivery and can store energy from wind or solar sources. Source: 11 Physics Book FBISE, p. 69.

21. Question 21

    Artificial gravity in a space station can be produced by:
    • AFiring its rockets forward
    • BRotating it about its axis
    • CMoving it closer to Earth
    • DIncreasing its total mass
    Show answer and explanation

    Answer: B) Rotating it about its axis

    The rim pushes on objects, providing the centripetal force (needs a = g). Source: 11 Physics Book FBISE, p. 72.

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