Tag: couple

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Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

State whether true or false.
A spanner with a longer handle can tighten nuts and bolts with less effort.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

We know, 

Moment of force = Force \times Distance between action point and force applied.
$\therefore T = F \times R$
As, R increases, T also increases.
So, we required to get less effort.

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

For a rigit body, we know that if verious forces act at various points in it , the resultant motion is as if a net force acts on the CM(centre of mass)  causing translation and a net torque at the CM causing rotation around an axis through the CM. for the earth-sun system (approximating the earth as a uniform density sphere).

  1. the torque is zero

  2. the torque causes the earth to spin

  3. the rigid body result is not applicable since the earth is not ever approximately a rigid body

  4. the torque causes the earth to move around the sun
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In the Earth-Sun system, the gravitational force acts on the Earth, and because the Earth is not a point mass but an extended body, the gravitational gradient creates a torque that contributes to the Earth's axial precession and spin dynamics.

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

The angular momentum of body remains conserve if:

  1. applied force on body is zero

  2. applied torque on body is zero.

  3. applied force on body is constant

  4. applied torque on body is constant.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Just as linear momentum is conserved when there is no net external forces$,$

angular momentum is constant or conserved when the net torque is zero$.$
Hence,
option $(B)$ is correct answer.

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

A body is acted upon by two forces each of magnitude $F$, but in opposite directions. State the effect of the forces if the two forces act at two different points of the body at a separation $r$. Which of the following is/are true?

  1. Resultant force $=0$

  2. moment of forces $=Fr$

  3. The forces tend to rotate the body about the mid-point between the two forces.

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Here we apply two forces of same magnitude but opposite in direction.Hence we have F and - F which makes resultant force as zero.


Moment of force for F is $r \times F $. For force F it has distance r therefore it has moment rF and same with force -F.Hence moment of force is rF.

The forces tend to rotate the body about the mid-point between the two forces.

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

Consider a cylindrical shaft of length $\lambda$ and radius $R$. It is twisted by torque r. If shear modulus of material is $S$, then angle of twist should be.

  1. $\theta =\dfrac { \pi SR^{ 4 } }{ 2\tau \ell } $

  2. $\theta =\dfrac { 2\tau }{ \pi S\ell S^{ 4 } } $

  3. $\theta =\dfrac { 2\tau \ell }{ \pi SR^{ 2 } } $

  4. $\theta =\dfrac { 2\tau \ell }{ \pi SR^{ 4 } } $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The formula for the angle of twist in a cylindrical shaft is theta = (2 * torque * length) / (pi * shear_modulus * radius^4).

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

A body is acted upon by two unequal forces in opposite directions, but not in same line. The effect is that:

  1. the body will have only the rotational motion.

  2. the body will have only the translational motion.

  3. the body will have neither the rotational motion nor the translational motion.

  4. the body will have rotational as well as translational motion.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Due to unequal forces, the net force will act on the body, so the forces are unbalanced and the unbalanced forces cause a change in motion. This means body having translational motion.
There also be torque acting on the body due to unbalanced force. So there will be rotational motion too.