Tag: physics

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Questions Related to physics

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

A flexible chain of length 2m and mass 1 kg initially held in vertical position such that its lower end just touches a horizontal surfaces, is released from rest at time t=0, Assuming that any part of chain which strike the plane immediately comes to rest and that the portion of chain lying on horizontal surface does not form  any heap, the height of its center of mass above surface at any instant $t=1/\sqrt { 5 } $(before it completely comes to rest) is

  1. 1 m

  2. 0.5 m

  3. 1.5 m

  4. 0.25 m
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As the chain falls, the velocity of the falling part increases. The center of mass of the chain is determined by the position of the part still in the air and the part already on the surface, accounting for the loss of potential energy.

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

A metallic ball has spherical cavity at its centre. If the ball is heated, what happens to the cavity?

  1. its volume increases

  2. its volume decreases

  3. its volume remains unchanged

  4. its volume may decreased or increase depending upon the nature of metal
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Thermal expansion affects the entire material uniformly, including the boundaries of any cavities. As the metal expands outward, the cavity effectively expands as if it were made of the same material.

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

A body having it's center of mass  at the origin. Then,

(The question having a multiple answers).

  1. x co-ordinates of the particles may be all positive.

  2. total KE must be conserved.

  3. total KE must very.

  4. total momentum shall vary.
Reveal answer Fill a bubble to check yourself
C,D Correct answer
Explanation

If all the particles have positive x  co-ordinates then their COM can't be at the origin. Total KE may not be conserved because of internal forces. Its not given that there is no external force acting on the system, so its momentum may also change.

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

Where will be the centre of mass on combining two masses $m$ and $M(M>m)$ ?

  1. $Towards \ m$
  2. $Towards \ M$
  3. $ exactly \ between \ m \ and \ M $
  4. $None \ of \ the \ above$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

As we can see that the center of mass will be at $r _c=\dfrac{mr+MR}{m+M}$,


where $r$ and $R$ are the position of the masses $m$ and $M$ respectively.

From the formula we notice that it will be between $m$ and $M$ and $nearer $ to the higher mass $M$.

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

A body has its center of mass at the origin. The x-axis coordinates of the particles :

  1. may be all positive

  2. may be all negative

  3. should be all at zero

  4. may be positive for some case and negative in other cases.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

All co-ordinates positive will make the co-ordinate of com positive.
All co-ordinates negative will make the co-ordinates of com negative.
If all the co-ordinates are zero(0), co-ordinate of com is zero(0).
If  co-ordinate of com can be zero,  co-ordinates of some are positive and co-ordinates of some are negative.

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

If the linear density of a rod of length L varies as $\lambda =A+B _x$, compute its centre of mass.

  1. $[\cfrac {L(3A+2BL)}{3(2A+BL},0,0]$
  2. $[0,\cfrac {(3A+2B)L}{(2A+3L},\cfrac L 2]$
  3. $[0,0\cfrac {L(3A+2BL)}{3(2A+BL}]$
  4. $[\cfrac L 2,00]$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The center of mass for a non-uniform rod is found by integrating x*lambda*dx divided by the total mass. With lambda = A + Bx, the integral of x(A+Bx) from 0 to L yields the numerator, and the integral of (A+Bx) yields the denominator.

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

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 

  1. $\dfrac{R}{4 \pi - 1}$
  2. $\dfrac{R}{2(4 \pi - 1)}$
  3. $\dfrac{R}{3(4 \pi - 1)}$
  4. $\dfrac{R}{4(4 \pi - 1)}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The shift in the center of mass is calculated using the principle of negative mass. The mass of the removed square is proportional to its area, and the shift is (m_removed * distance) / (M_total - m_removed).

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

Which of the following is not correct about 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
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

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

  1. centre of gravity

  2. centre of mass

  3. centre of force

  4. centre of acceleration
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The center of gravity is the point where the total gravitational force (weight) of a body is considered to act. While often coincident with the center of mass, the definition specifically refers to weight.

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

In classical system:

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Classical mechanics is a broad framework that can accommodate varying mass systems, such as rockets or chains, through the application of Newton's second law in the form F = dp/dt.