Tag: turning effects of forces

Questions Related to turning effects of forces

If a square of side $\dfrac{R}{2}$ is removed from a uniform circular disc of radius R as shown in the figure, the shift in centre of mass is 

physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. $\dfrac{R}{4 \pi - 1}$

  2. $\dfrac{R}{2(4 \pi - 1)}$

  3. $\dfrac{R}{3(4 \pi - 1)}$

  4. $\dfrac{R}{4(4 \pi - 1)}$

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Correct Option: B

Which of the following is not correct about centre of mass ?

physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. It depends on the choice of frame of reference

  2. In centre of mass frame, momentum of a system is always zero

  3. Internal forces may affect the motion of centre of mass

  4. Centre of mass and centre of gravity coincide in uniform gravitational field

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Correct Option: C
Explanation:

The internal forces all balance each other so that there is no change in the mass distribution of the body, thus center of mass remains unchanged. Rest all options are correct.

A point at which a whole weight of body act vertically downward is ________.

physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. centre of gravity

  2. centre of mass

  3. centre of force

  4. centre of acceleration

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Correct Option: A

In classical system:

physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. the varying mass system is not considered

  2. the varying mass system must be considered

  3. the varying mass system may be considered

  4. only varying of mass due to velocity is considered

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Correct Option: C

Statement 1: When we lean behind over the hind legs of the chair, the chair falls back after a certain angle.

Statement 2: Centre of mass lying outside the system makes the system unstable.

physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. Statement 1 is false, Statement 2 is true

  2. Statement 1 is true, Statement 2 is true; Statement 2 is a correct explanation for Statement 1

  3. Statement 1 is true, Statement 2 is true; Statement 2 is not a correct explanation for Statement 1

  4. Statement 1 is true, Statement 2 is false

Show answer
Correct Option: D
Explanation:
The chair falls down after a certain angle because it becomes unstable as the normal reaction by ground on chair becomes zero.
There are several mechanical structure whose COM lies outside its body but they are quite stable.

So option D is correct.

On a stationary sail boat, air is blown at the sails from a fan attached to the boat. The boat will

physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. remain at rest

  2. spin round

  3. move in the direction in which air is blown

  4. move in a direction opposite to that in which air is blown

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Correct Option: A
Explanation:

the boat will remain at the rest  because the thrust or recoil force of fan at boat and force of air on the sails will cancel each other and boat will not at all move .

so the answer is A.

The passengers in a boat are not allowed to stand because: 

physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. This will raise the centre of gravity and the boat will be rocked

  2. This will lower centre of gravity and the boat will rocked

  3. The effective weight of system increases

  4. Of surface tension effects

Show answer
Correct Option: A
Explanation:

when passengers stands up on the boat from the sitting situation , the centre of gravity moves upwards and it increases the chances of toppling of boat .

so the answer is A.

State whether true or false.
The centre of gravity of regular shaped objects is at their geometric centre.
physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. True

  2. False

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Correct Option: A
Explanation:

The given statement is true that centre of gravity of rectangular shaped objects is at their geometric centre.

The point through which the total weight of an object appears to act for any orientation of the object is ______.

physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. Centre of buoyancy

  2. Centre of gravity

  3. Centre of curvature

  4. Median of a triangle

Show answer
Correct Option: B
Explanation:

The point through which the total weight of an object appears to act for any orientation of the object is centre of gravity.

State whether true or false.
The position of centre of gravity of an object depends on the acceleration due to gravity at the given place.
physics turning effects of forces stability and centre of mass center of mass centre of mass

  1. True

  2. False

Show answer
Correct Option: B
Explanation:
The center of gravity is a geometric property of any object. The center of gravity is the average location of the weight of an object with mass.
Therefore the position of centre of mass has nothing to do with the acceleration due to gravity.
So, the statement is FALSE