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Circular and Rotational Motion MCQs — Physics (page 8)

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.

176. A disc's angular velocity changes from 50 rad/s to 0 rad/s in 10 s. Its angular acceleration is:

  1. -5 rad/s^2
  2. 5 rad/s^2
  3. -10 rad/s^2
  4. -2.5 rad/s^2

Answer: A) -5 rad/s^2

Explanation: alpha = omegaf - omegait = -5 rad/s^2. SLO P-11-B-08 · Understanding

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177. A person in a lift feels weightless when:

  1. the lift falls freely with acceleration g
  2. the lift moves up at constant speed
  3. the lift accelerates upward
  4. the lift is at rest

Answer: A) the lift falls freely with acceleration g

Explanation: Then the floor exerts no force. SLO P-11-B-16 · Understanding

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178. A point is 2 m from the axis of a wheel rotating at 3 rad/s. Its centripetal acceleration is:

  1. 6 m/s^2
  2. 18 m/s^2
  3. 9 m/s^2
  4. 36 m/s^2

Answer: B) 18 m/s^2

Explanation: a = romega^2 = (2)(3)^2 = 18 m/s^2. SLO P-11-B-08 · Understanding

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179. A wheel starts at 10 rad/s with angular acceleration 2 rad/s^2. After 6 s its angular velocity is:

  1. 11 rad/s
  2. 13 rad/s
  3. 44 rad/s
  4. 22 rad/s

Answer: D) 22 rad/s

Explanation: omegaf = omegai + alpha t = 10 + (2)(6) = 22 rad/s. SLO P-11-B-09 · Application

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180. A charged particle moving at right angles to a uniform magnetic field moves in a circle because:

  1. the field does work on it
  2. the force is parallel to its velocity
  3. the magnetic force is always perpendicular to its velocity
  4. its charge changes

Answer: C) the magnetic force is always perpendicular to its velocity

Explanation: A perpendicular force provides centripetal force. SLO P-11-B-10 · Understanding

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181. For the same torque, a body with a larger moment of inertia has:

  1. zero angular velocity
  2. the same angular acceleration
  3. a larger angular acceleration
  4. a smaller angular acceleration

Answer: D) a smaller angular acceleration

Explanation: alpha = tau/I. SLO P-11-B-19 · Application

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182. A flywheel speeds up from 0 rad/s to 20 rad/s while turning through 50 rad. Its angular acceleration is:

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

Answer: D) 4 rad/s^2

Explanation: omegaf^2 = omegai^2 + 2alphatheta Rightarrow alpha = 20^2 - 0^22(50) = 4 rad/s^2. SLO P-11-B-09 · Application

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183. Gyroscopes are used in:

  1. electric kettles
  2. light bulbs
  3. navigation systems of ships, aircraft and phones
  4. thermometers

Answer: C) navigation systems of ships, aircraft and phones

Explanation: They sense rotation and keep a reference direction. SLO P-11-B-20 · Application

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184. One radian is the angle subtended at the centre by an arc:

  1. equal to the diameter
  2. of length 1 cm
  3. equal to the circumference
  4. equal in length to the radius

Answer: D) equal in length to the radius

Explanation: theta = s/r = 1 when s = r. SLO P-11-B-07 · Understanding

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185. A bucket of water is swung in a vertical circle of radius 1 m. The minimum speed at the top so the water stays in is (g = 9.8 m/s^2):

  1. 3.13 m/s
  2. 1.57 m/s
  3. 6.26 m/s
  4. 4.43 m/s

Answer: A) 3.13 m/s

Explanation: At the minimum speed, weight alone provides the centripetal force: mg = mv^2r Rightarrow v = gr = 3.13 m/s. SLO P-11-B-15 · Application

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186. Increasing the rotation speed of a centrifuge:

  1. increases the separating effect as omega^2
  2. decreases separation
  3. reverses separation
  4. has no effect

Answer: A) increases the separating effect as omega^2

Explanation: a = romega^2. SLO P-11-B-21 · Application

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