Tag: forces - vectors and moments

Quizzes (8) Questions (83)

Questions Related to forces - vectors and moments

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

An object can have 

  1. more than one center of gravity.

  2. only one center of gravity 

  3. always two center of gravity

  4. none of the above 
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Centre of gravity of an object is a specific point such that the body behaves as if the entire gravitational force is acting only at that point. It is unique for an object and can't be more than 1.

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

The centre of mass of a system of particles is at the origin. From this we conclude that :

  1. The numberof particles on positive x-axis is equal to the number of particles on negative x-axis

  2. The total mass of the particles on positive x-axis is same as the total mass on negative x-axis

  3. The number of particles on X-axis may be equal to the number of particles on Y-axis.

  4. If there is a particle on the positive X-axis, there must be at least one particle in the negative X - axis.:
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Given :  The COM of the system  is at origin   i.e  $X = 0$
Let the position of particle of mass $m _1$ on the positive axis be  $a$.
Using       $X = \dfrac{m _1x _1+m _2x _2}{m _1+m _2}$
$\therefore$   $0 = \dfrac{m _1a+m _2x _2}{m _1+m _2}$              $\implies x _2 = -\dfrac{m _1}{m _2}a$
This implies that for a particle on the positive X axis, there must be at least one particle particle in the negative X axis.
Multiple choice physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

A book is lying on a table, what is the angle between the book on the table and the weight of the book?

  1. $0^o$

  2. $45^o$

  3. $90^o$

  4. $180^o$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Weight always point towards the center of the earth that is perpendicular to the surface of the earth that is towards the table and $perpendicular$ to surface of the table.


Now as the book is lying on the table i.e. book is $parallel$ to the table and the weight is perpendicular to the table so the required angle is $90^0$
Option C is correct.

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

The center of gravity of an object 

  1. can never exist at a point where there is no mass.

  2. <span>can exist at a point where there is no mass.</span>

  3. may exist or may not exist.

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Centre of gravity of an object is a specific point such that the body behaves as if the entire gravitational force is acting only at that point. It is unique for an object and can't be more than 1.

There are some objects whose centre of gravity doesn't have any matter at it. Eg: A hollow sphere and a ring have their centres of gravity at their geometric centres. 

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

The centre of gravity of an object is ______ whether it is placed near the surface of the Earth or near the surface of the Moon.

  1. <span>same&nbsp;</span>

  2. different&nbsp;

  3. depend on the situation

  4. none
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Centre of mass is a point on a physical body which behaves as if the whole mass is concentrated over there. Whenever a force acts on a body it appears to be acting on the centre of mass. Whenever gravitational force is acting on a body it appears to be acting on a specific point on the body which is known as the centre of gravity.
 It usually coincides with the centre of mass. Earth being a larger planet than the moon, the gravitational force is more intense on earth as compared to the moon.
 The location of the centre of mass does not vary with the intensity of the force acting on the body. Similarly, centre of gravity does not vary with the intensity of the gravitational force acting on it.  Hence the centre of gravity on earth and moon will be the same

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

The center of gravity of an object is 

  1. the sum of its moments divided by the weight of the specific object.

  2. the sum of its moments divided by the overall weight of the object.

  3. the sum of its moments of product of the overall weight of the object.

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The center of gravity is defined as the ratio of sum of its moments to the total weight of the object.

Mathematically, center of gravity  $x = \dfrac{m _1 g x _1 + m _2 g x _2 +....m _n g x _n}{(m _1 + m _2 + .....m _n) g}$
$\implies$  $x = \dfrac{m _1  x _1 + m _2  x _2 +.... m _n x _n}{M}$
where overall weight of object $M = m _1 + m _2 +...m _n$