Tag: turning effect of force

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Multiple choice physics forces - vectors and moments the turning of couple couple rotational motion of a rigid body and moment of inertia turning effect of force

If a car is moving forward, what is the direction of the moment of the moment caused by the rotation of the tires

  1. It is heading inwards, i.e. the direction is towards inside of the car

  2. It is heading outwards, i.e. the direction is towards outside of the car

  3. It is heading forward, i.e. the direction is towards the forward direction of the motion of the car

  4. It is heading backward, i.e. the direction is towards back side of the motion of the car
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Multiple choice physics forces - vectors and moments the turning of couple couple rotational motion of a rigid body and moment of inertia turning effect of force

Which of the following is/are the properties of moment of a couple?

  1. It tends to produce pure rotation.

  2. It is different about any point in the plane of lines of action of the forces.

  3. It can be replaced by any other couple of the same moment.

  4. The resultant of set of two or more couples is equal to the sum of the moments of the individual couples.
Reveal answer Fill a bubble to check yourself
A,C,D Correct answer
Explanation

A couple when applied to a body it produce 

(i) Pure rotation
(ii) It can be replaced by any other couple of same moment.
(iii) The resultant of set of two or more couples is equal to the sum of moment of individuals couples.

Multiple choice physics forces - vectors and moments the turning of couple couple rotational motion of a rigid body and moment of inertia turning effect of force

Two like parallel forces $20\ N$ and $30\ N$ act at the ends $A$ and $B$ of a rod $1.5\ m$ long. The resultant of the forces will act at the point:

  1. $90\ cm$ from A

  2. $75\ cm$ from B

  3. $20\ cm$ from B

  4. $85\ cm$ from A
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Consider the point at which resultant of the forces will act, is 'x' m from the point A.

Thus the point is (1.5 - x) m far from the point B.

Thus, using the formula Torque = Distance x Force acting

$20x = 30(1.5 - x)$

or,$ 2x = 4.5 - 3x$

or,$ 5x = 4.5$

or, $x = 0.9m or 90cm$

Thus the resultant point will be 0.9 m or 90 cm far from point A

Multiple choice physics forces - vectors and moments the turning of couple couple rotational motion of a rigid body and moment of inertia turning effect of force

Two small kids weighing 10kg and 15kg are trying to balance a seesaw of total length 5m with the fulcrum at the centre. If one of the kids is sitting at an end, the other should sit at

  1. 1.7 m from the centre

  2. 2.5 m from the centre

  3. 2 m from the centre

  4. 1 m from the centre
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For the seesaw to balance, the torques must be equal: 10kg * x = 15kg * (2.5m - x). Solving this gives 10x = 37.5 - 15x, so 25x = 37.5, which means x = 1.5m from the center. None of the options match exactly, but 1.7m is the closest provided.

Multiple choice physics forces - vectors and moments the turning of couple couple rotational motion of a rigid body and moment of inertia turning effect of force

A couple produces

  1. Linear motion

  2. Rotational motion

  3. Both $A$ and $B$

  4. Nether $A$ nor $B$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A couple consists of two parallel forces that are equal in magnitude, opposite in sense and do not share a line of action. It does not produce any translation, but only rotational motion.

Multiple choice physics forces - vectors and moments the turning of couple couple rotational motion of a rigid body and moment of inertia turning effect of force

A couple is acting on a two particle systems. The resultant motion will be

  1. Purely rotational motion

  2. Purely linear motion

  3. Both $A$ and $B$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A couple consists of two equal and opposite forces whose lines of action are parallel and laterally separated by the some distance. Therefore, net force (or resultant) of a couple is null vector, hence there is no translational acceleration, only rotational motion will be there.

Multiple choice physics forces - vectors and moments the turning of couple couple rotational motion of a rigid body and moment of inertia turning effect of force

In case of torque of a couple, if the axis is changed by displacing it parallel to itself, torque will

  1. Increase

  2. Decrease

  3. Remain constant

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Torque of a couple   $\tau = d\times F$
where  $d$ is the distance between the two equal force $F$
Thus, the distance between the forces remains the same even on changing the axis. So, the torque will remain the same.
Multiple choice physics forces - vectors and moments the turning of couple couple rotational motion of a rigid body and moment of inertia turning effect of force

A couple produces :

  1. no motion

  2. linear and rotational motion

  3. purely rotational motion

  4. purely linear motion
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A couple consists of two equal and opposite forces acting at a separation, so that net force becomes zero. When a couple acts on a body it rotates the body but does not produce any translatory motion. Hence, only rotational motion is produced.