MCQs / Physics / Circular and Rotational Motion

Circular and Rotational Motion MCQs — Physics

186 multiple-choice questions on Circular and Rotational Motion from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

1. A body completes one revolution every 86,400 s. Its angular velocity is:

  1. 1.16 10^-5 rad/s
  2. 1.45 10^-4 rad/s
  3. 3.64 10^-5 rad/s
  4. 7.27 10^-5 rad/s

Answer: D) 7.27 10^-5 rad/s

Explanation: omega = 2piT = 2pi86,400 = 7.27 10^-5 rad/s. (This is the Earth's rotation.) SLO P-11-B-08 · Understanding

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2. The radian is:

  1. the same as a degree
  2. a dimensionless ratio of two lengths
  3. a unit of length
  4. an SI base unit

Answer: B) a dimensionless ratio of two lengths

Explanation: theta = s/r: metre/metre. SLO P-11-B-07 · Understanding

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3. The artificial gravity felt by an astronaut standing on the rim is equal to:

  1. romega
  2. omega^2/r
  3. romega^2
  4. omegar

Answer: C) romega^2

Explanation: Centripetal acceleration. SLO P-11-B-17 · Understanding

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4. A 3 kg mass rotates at 4 rad/s on a radius of 2 m. The centripetal force is:

  1. 48 N
  2. 24 N
  3. 192 N
  4. 96 N

Answer: D) 96 N

Explanation: F = mromega^2 = 3 2 4^2 = 96 N. SLO P-11-B-14 · Application

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5. A 2 kg body moves at 5 m/s in a circle of radius 1 m. The centripetal force is:

  1. 25 N
  2. 100 N
  3. 50 N
  4. 10 N

Answer: C) 50 N

Explanation: F = mv^2r = 2 5^21 = 50 N. SLO P-11-B-14 · Application

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6. Doubling the rpm of a centrifuge makes the acceleration:

  1. double
  2. unchanged
  3. four times as large
  4. half

Answer: C) four times as large

Explanation: a propto omega^2. SLO P-11-B-21 · Application

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7. Weightlessness affects astronauts' bodies by:

  1. making them heavier
  2. stopping their heart
  3. increasing their mass
  4. weakening muscles and bones over long missions

Answer: D) weakening muscles and bones over long missions

Explanation: Muscles and bones aren't loaded. SLO P-11-B-16 · Understanding

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8. Why is a door handle placed far from the hinges?

  1. it reduces the moment of inertia
  2. it increases friction
  3. a larger lever arm gives more torque for the same force
  4. it looks better

Answer: C) a larger lever arm gives more torque for the same force

Explanation: tau = rF. SLO P-11-B-19 · Application

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9. A satellite in orbit is continuously:

  1. pushed by its engines
  2. at rest relative to the Earth's centre
  3. falling towards the Earth but moving sideways fast enough to miss it
  4. escaping from the Earth

Answer: C) falling towards the Earth but moving sideways fast enough to miss it

Explanation: Newton's cannonball picture of orbits. SLO P-11-B-16 · Understanding

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10. A flywheel speeds up from 10 rad/s to 30 rad/s while turning through 100 rad. Its angular acceleration is:

  1. 4 rad/s^2
  2. 8 rad/s^2
  3. 2 rad/s^2
  4. 5 rad/s^2

Answer: A) 4 rad/s^2

Explanation: omegaf^2 = omegai^2 + 2alphatheta Rightarrow alpha = 30^2 - 10^22(100) = 4 rad/s^2. SLO P-11-B-09 · Application

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11. Artificial gravity is needed on long space missions mainly to:

  1. prevent loss of bone and muscle
  2. protect from radiation
  3. make fuel last longer
  4. keep the station in orbit

Answer: A) prevent loss of bone and muscle

Explanation: The body needs loading. SLO P-11-B-17 · Understanding

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12. A 1200 kg body moves at 15 m/s in a circle of radius 100 m. The centripetal force is:

  1. 2700 N
  2. 180 N
  3. 5400 N
  4. 1350 N

Answer: A) 2700 N

Explanation: F = mv^2r = 1200 15^2100 = 2700 N. SLO P-11-B-14 · Application

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13. The SI unit of torque is:

  1. rad/s^2
  2. N m
  3. kg m^2
  4. J/s

Answer: B) N m

Explanation: Force × distance (not called joule because it isn't energy). SLO P-11-B-19 · Application

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14. If the speed of a body in a circle is doubled (same radius), the centripetal force becomes:

  1. half
  2. 4 times as large
  3. unchanged
  4. 2 times as large

Answer: B) 4 times as large

Explanation: F propto v^2. SLO P-11-B-14 · Application

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15. A force that always acts perpendicular to a body's velocity changes:

  1. neither
  2. its speed but not its direction
  3. its direction but not its speed
  4. both speed and direction

Answer: C) its direction but not its speed

Explanation: A perpendicular force does no work, so kinetic energy (speed) stays the same. SLO P-11-B-10 · Understanding

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16. A wheel accelerates uniformly from rest at 2 rad/s^2. The time it takes to reach 30 rad/s is:

  1. 15 s
  2. 60 s
  3. 28 s
  4. 7.5 s

Answer: A) 15 s

Explanation: t = omegaf - omegaialpha = 302 = 15 s. SLO P-11-B-09 · Application

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17. A solid disc and a ring of the same mass and radius receive the same torque. The disc's angular acceleration is:

  1. equal to the ring's
  2. four times the ring's
  3. twice the ring's
  4. half the ring's

Answer: C) twice the ring's

Explanation: Idisc = 12MR^2 = 12Iring, and alpha = tau/I. SLO P-11-B-19 · Application

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18. A centrifuge speeds up separation compared with letting a mixture settle because:

  1. it removes gravity
  2. it cools the mixture
  3. it produces an effective 'gravity' thousands of times g
  4. it removes air

Answer: C) it produces an effective 'gravity' thousands of times g

Explanation: romega^2 gg g. SLO P-11-B-21 · Application

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19. If the perpendicular force on a moving body is increased (same speed), its path:

  1. is unchanged
  2. curves more sharply (smaller radius)
  3. becomes a spiral outward
  4. becomes straighter

Answer: B) curves more sharply (smaller radius)

Explanation: r = mv^2/F. SLO P-11-B-10 · Understanding

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20. A ring of mass 2 kg and radius 0.5 m rotates about its central axis. Its moment of inertia is:

  1. 0.4 kg m^2
  2. 0.25 kg m^2
  3. 1 kg m^2
  4. 0.5 kg m^2

Answer: D) 0.5 kg m^2

Explanation: I = MR^2 = 0.5 kg m^2. SLO P-11-B-18 · Application

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21. The SI unit of centripetal force is:

  1. joule
  2. newton
  3. watt
  4. rad/s

Answer: B) newton

Explanation: It is a force. SLO P-11-B-14 · Application

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22. An arc of length 15 m on a circle of radius 5 m subtends an angle of:

  1. 6 rad
  2. 172 rad
  3. 3 rad
  4. 1.5 rad

Answer: C) 3 rad

Explanation: theta = sr = 155 = 3 rad. SLO P-11-B-07 · Understanding

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23. On a level road, if the coefficient of friction is halved, the maximum safe speed on a bend:

  1. is unchanged
  2. halves
  3. doubles
  4. is divided by 2

Answer: D) is divided by 2

Explanation: v = mu g r. SLO P-11-B-15 · Application

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24. A passenger on a merry-go-round is kept in a circle by:

  1. gravity alone
  2. air pressure
  3. a centrifugal force
  4. friction and the push of the seat/handrail towards the centre

Answer: D) friction and the push of the seat/handrail towards the centre

Explanation: Something must push inward. SLO P-11-B-15 · Application

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25. A car rounds a flat bend of radius 50 m. The coefficient of friction is 0.8 (g = 9.8 m/s^2). The maximum safe speed is:

  1. 28 m/s
  2. 9.9 m/s
  3. 39.6 m/s
  4. 19.8 m/s

Answer: D) 19.8 m/s

Explanation: Friction provides the centripetal force: mu mg = mv^2r Rightarrow v = mu g r = 19.8 m/s. SLO P-11-B-15 · Application

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