Tag: turning effect of force

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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

It becomes easier to open or close a door turning about its hinges if the force is applied at the:

  1. Two third of the door

  2. Free edge of the door

  3. Middle of the door

  4. Point near the hinges
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Torque acting about any point O         $\tau _o = rF$                 for $sin\theta = 1$

where $r$ is the distance of the application of force from point O.
As  $r$ is maximum when a force is applied at the free end of the door, thus less amount of force is required to produce the same torque. Hence it is easier to open or close the door if force is applied at its free end. 

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).