Tag: turning effects of forces

Questions Related to turning effects of forces

If the earth shrinks such that its mass does not change but radius decreases to one quarter of its original value then one complete day will take:

physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

  1. 96 h

  2. 48 h

  3. 6 h

  4. 1.5 h

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Correct Option: D
Explanation:

We know that angular momentum of spin $\displaystyle =I\omega $
Bythe conservation of angular momentum
$\displaystyle \frac { 2 }{ 5 } M{ R }^{ 2 }.\frac { 2\pi  }{ T } =\frac { 2 }{ 5 } M{ \left( \frac { R }{ 4 }  \right)  }^{ 2 }.\frac { 2\pi  }{ T' } $
$\displaystyle T'=\frac { T }{ 16 } =\frac { 24 }{ 16 } =1.5h$

Weight $W _ { m }$ of the body can be given as 

physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

  1. $m g - m \frac { \left( v _ { e } + v \right) ^ { 2 } } { R }$

  2. $m g - m \frac { \left( v _ { e } - v \right) ^ { 2 } } { R }$

  3. $\frac { m } { R } \left[ v _ { e } ^ { 2 } - \left( v _ { e } + v \right) ^ { 2 } \right]$

  4. $m g + m \frac { \left( v _ { e } + v \right) ^ { 2 } } { R }$

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Correct Option: A

Why are the passengers in the upper deck of a double-decker bus not allowed to stand?

physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

  1. This ensures that the centre of gravity of the system may not rise up and the bus may not be toppled due to unstable equilibrium

  2. This ensures smaller centripetal force, thus helping the driver to negotiate the roundabouts properly

  3. If the passengers are in standing position, they may start oscillating due to jerks and there is a possibility of resonance, causing the bus to be toppled

  4. This is just for the safety reason

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Correct Option: A
Explanation:

When the passengers stand, the center of gravity rises. If it rises much it becomes unstable and may topple down.

Can the centre of gravity be situated outside the material of the body ?

physics forces - vectors and moments centre of gravity turning effects of forces acceleration due to gravity

  1. Yes

  2. No

  3. Can't say

  4. None

Show answer
Correct Option: A
Explanation:

Yes, it can. For example, in case of a ring, it is situated at the centre of that circle. But the material is only along the circumference. Hence centre of gravity is situated outside the material of the body.

Reference to ability of an object to return to its original position after it has been tilted slightly is termed as:

physics forces - vectors and moments centre of gravity turning effects of forces acceleration due to gravity

  1. Stability

  2. Equilibrium

  3. Centre of gravity

  4. Torque

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Correct Option: A
Explanation:

stability of an object depends on the ability of an object to return back to its original equlibirum, when disturbed

If you place pivot at center of a meter rule, weight has no

physics forces - vectors and moments centre of gravity turning effects of forces acceleration due to gravity

  1. property

  2. Concern

  3. Turning effect

  4. Magnitude

Show answer
Correct Option: C
Explanation:

The weight of an object is concentrated at the centre of gravity and hence a pivot at the centre of the metre scale does not record any changes in mass. Hence the scale does not turn around

What is the position of centre of gravity of a cylinder?

physics motion of system of particles and rigid bodies centre of gravity turning effects of forces forces - vectors and moments

  1. At the center of base circle

  2. At the center of top circle

  3. Cannot be determined

  4. At the mid point on the axis of cylinder

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Correct Option: D
Explanation:

Centre of gravity means a point from which the weight of a body or system may be considered to act. In uniform gravity it is the same as the centre of mass. For regular shaped bodies it lies at the centre of the that particular body. Hence for a cylinder centre of gravity lies at the midpoint of the axis of the cylinder.

In an artificial satellite, the use of a pendulum watch is discarded, because :

physics motion of system of particles and rigid bodies centre of gravity turning effects of forces forces - vectors and moments

  1. The satellite is in a constant state of motion

  2. The effective value of $g$ becomes zero in the artificial satellite

  3. The periodic time of the pendulum watch is reduced

  4. None of these

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Correct Option: B

Given that there is a relationship between the orbital radius of a planet and its period of revolution and that the periods of revolution of Mercury, Earth, Jupiter and Neptune and nearly 0.24, 1, 11.8 and 165 years. It follows that the period of revolution of
1. Venus is less than 0.24 years
2. Mars is less than 12 years
3. Uranus is more than 165 years
4. Uranus is less than 165 years but more than 12 years.

physics motion of system of particles and rigid bodies centre of gravity turning effects of forces forces - vectors and moments

  1. 1 and 3

  2. 4 only

  3. 3 o nly

  4. 2 and 4

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Correct Option: D