Tag: physics

Questions Related to physics

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

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

  1. Two third of the door

  2. Free edge of the door

  3. Middle of the door

  4. Point near the hinges

Show answer
Correct Option: B
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. 

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

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

  1. True

  2. False

Show answer
Correct Option: A
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.

Which of the following playground equipment make use of the turning effect of forces?

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

  1. See-saw

  2. Slide

  3. Swing

  4. Toy horse

Show answer
Correct Option: A,C,D
Explanation:

See-saw, Swing and Toy horse are the playground equipment make use of the turning effect of forces.

The spanner with a longer handle can tighten nuts and bolts with less effort.

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

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

spanner with longer handle needs less force to generate same torque than with spanner with short handle .

so the answer is A.

Self balancing toys have curved and heavy base area.

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

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

if the base area will be heavy than the centre of gravity will be near to ground and if the base area is curved than the object will come in its balanced position everytime due gravitational torque.

so the answer is A.

Which of the following sports uses the turning effect of forces?

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

  1. Cycling

  2. Swimming

  3. Badminton

  4. Hockey

Show answer
Correct Option: A,B,C,D
Explanation:

cycling , swimming , badminton and hockey all these sports makes use of turning effect  of forces while play. 

so the answer is A,B,C and D .

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).

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

  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

Show answer
Correct Option: B

The angular momentum of body remains conserve if:

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

  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.

Show answer
Correct Option: B
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.

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?

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

  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

Show answer
Correct Option: D
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.

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.

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

  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 } } $

Show answer
Correct Option: D