Physics

Rotational and Circular Motion

235 Questions

Rotational and circular motion examines the dynamics of objects moving in circular paths or rotating around an axis. Key concepts include angular momentum, torque, moment of inertia, and centripetal force. This is a highly scoring topic in the physics section of competitive exams.

Angular momentumCentripetal forceMoment of inertiaRolling objectsGyroscopic effect

Rotational and Circular Motion Questions

Multiple choice general knowledge

Formula for centripetal force v:tangential velocity m:mass r:radius?

  1. v^2/mr

  2. mv^2/r

  3. r^2m/v

  4. mv/r
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The centripetal force formula is F = mv^2/r, where m is mass, v is tangential velocity, and r is the radius of the circular path. This force is directed toward the center of the circle and keeps the object moving in circular motion. Option A has the division reversed, option C has incorrect variables, and option D is missing the squared velocity term.

Multiple choice general knowledge science & technology

Angular Speed

  1. ? r

  2. m ?

  3. ¾ ? r

  4. m ?2
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Angular speed (ω) is calculated as linear speed (v) divided by radius (r), giving ω = v/r. The formula relates the tangential velocity of a point on a rotating object to its distance from the center. Option A shows this relationship.

Multiple choice general knowledge science & technology

If a disc is rotating with a angular velocity of w radians per sec. What is the speed of the disc in RPM.

  1. ( 2 x pi x w)/ 60

  2. (60 x w)/(2 x pi)

  3. 2 x pi x w

  4. w x 60
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

To convert from radians per second to RPM, multiply by 60 (to get radians per minute) and divide by 2pi (since one revolution is 2pi radians). RPM = (w × 60) / (2pi). Option A would give radians per hour, while options C and D are incomplete conversions.

Multiple choice general knowledge

An object starts moving in a circular path of radius R. What is the distance and displacement respectively, if the object is at the diametrically opposite point from the starting point.

  1. 2 pi R , 2 pi R

  2. pi R , pi R

  3. pi R , 2R

  4. pi R , zero
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When an object moves to the diametrically opposite point on a circle, it travels half the circumference: distance = πR. Displacement is the straight-line distance from start to end, which is the diameter: 2R. Distance is path length traveled, displacement is shortest distance between points.

Multiple choice general knowledge science & technology

A ball attached to a string is rotating in horizontal circle. If the string breaks the the direction in which ball goes is __ .

  1. it moves radially inwards.

  2. it moves radially outward.

  3. it can move in any direction.

  4. it moves in direction of tangent at the point of break.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When a ball rotates in a horizontal circle, it has centripetal acceleration directed toward the center, provided by string tension. When the string breaks, this centripetal force vanishes. According to Newton's first law, the object continues in its current velocity direction - the tangent to the circle at the point of release. It does not fly radially outward (a common misconception), as that would require a force in that direction.

Multiple choice general knowledge math & puzzles

If you balanced a broom horizontally on your finger, so that your finger was exactly on the broom's center of gravity, marked that spot and cut the broom in half then you would have a long and a short piece. The long piece being most of the handle and the

  1. Your mom will find out and hit you with both pieces!

  2. Both will weigh the same.

  3. The long piece will weigh more.

  4. The short piece will weigh more.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

At the center of gravity, both halves have equal torque (weight × distance). Since the long piece has greater distance from the balance point, it must have less weight to maintain balance. The short piece has more mass concentrated closer to the center, making it heavier despite being shorter.

Multiple choice general knowledge science & technology

In a uniform circular motion the acceleration acts towards...

  1. tangent to circle

  2. centre of circle

  3. can act in any direction

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In uniform circular motion, acceleration is centripetal - it always points toward the center of the circular path. This acceleration is responsible for continuously changing the direction of velocity to maintain circular motion, not the tangent (which would be the velocity direction).

Multiple choice general knowledge science & technology

what is the relation between angular speed and velocity with reference to circular motion?

  1. v = r*w*w

  2. v = r/w

  3. v = r*w

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In circular motion, linear velocity v equals radius r multiplied by angular velocity w (v = rw). This relationship holds because angular velocity w is defined as the rate of change of angle, and the arc length traveled is r times the angle.

Multiple choice

A solid sphere, a disc and a ring of the same mass and radius are allowed to role down a frictionless inclined plane simultaneously from the same height. In this context, which one of the following statements is correct?

  1. The disc reaches down first

  2. The sphere reaches down first

  3. The ring reaches down first.

  4. All of them reach down simultaneously
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For rolling without slipping, acceleration depends on moment of inertia: a = g*sin(θ) / (1 + I/mr²). Sphere has lowest I (2/5 MR²), giving highest acceleration ~0.714g*sin(θ). Disc has I = 1/2 MR² (acceleration ~0.667g*sin(θ)). Ring has highest I = MR² (acceleration ~0.5g*sin(θ)). Sphere reaches bottom first.

Multiple choice

A glass ball is weighed by a brass weight. Which of the following will happen, if the system is kept in vacuum?

  1. The beam scale will remain horizontal.

  2. Pan of glass ball will rise.

  3. Pan of glass ball will decrease.

  4. Depends on the amount of air extracted.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Glass has lower density than brass, so in air it experiences greater buoyant force. In vacuum, buoyancy disappears, reducing the upward force on the glass side more than the brass side, making the glass pan go down (decrease).

Multiple choice

A particle moves in a circle of radius R with a constant speed under a centripetal force F. The magnitude of work done in completing a full circle will be-

  1. 2RF

  2. πR2F

  3. 2πRF

  4. Zero
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work done is zero because centripetal force is always perpendicular to the displacement of the particle. Since work = F × d × cos(θ) and θ = 90° throughout circular motion, cos(90°) = 0, making work done zero regardless of the number of revolutions completed.

Multiple choice

Consider the following statements:

  1. When a body is in circular motion, work is said to be done by centripetal force.
  2. The hand flour grinder is provided with a handle near its rim to reduce the centre of gravity.

Which of the given statements is/are incorrect?

  1. Only (1)

  2. Only (2)

  3. Both (1) & (2)

  4. Neither (1) nor (2)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Statement (1) is wrong. When a body is in circular motion, no work is said to be done by centripetal force. Statement (2) is wrong. The hand flour grinder is provided with a handle near its rim, because the perpendicular distance of the line of action of the force from the axis of rotation will be maximum to get the largest turning effect.

Multiple choice

If a heavy suitcase is fitted with rollers, then it can be pulled very easily. It is because rollers convert

  1. sliding friction into rolling friction

  2. rolling friction into sliding friction

  3. static friction into sliding friction

  4. rolling friction into static friction

  5. sliding friction into static friction
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is the correct option. If a heavy suitcase is fitted with rollers, then it can be pulled very easily. It is because rollers convert sliding friction into rolling friction.