Assertion: A uniform cubical block (of side a ) undergoes translational motion on a smooth horizontal surface under action of horizontal force F as shown. Under the given condition, the horizontal surface exerts normal reaction non-uniformly on lower surface of the block. Reason: For the cubical block given in statement 1 , the horizontal force F has tendency to rotate the cube about its centre in clockwise sense. Hence, the lower right edge of cube presses the horizontal surface harder in comparison to the force exerted by lower left edge of cube on horizontal surface.

If Assertion is true but Reason is false.

If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

If both Assertion and Reason are false.

If F → be a force acting on a particle having the position vector r → and τ → be the torque of this force about the origin. Then

r → · τ → = 0 and F → · τ → = 0

r → × τ → = 0 and F → × τ → ≠ 0

r → × τ → ≠ 0 and F → × τ → ≠ 0

r → × τ → ≠ 0 and F → × τ → = 0

r → × τ → ≠ 0 and r → · τ → ≠ 0

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Assertion : If the momentum of a particle is constant, then its angular momentum will also be constant

Reason : When net external force on an object is zero, then external torque on the object will also be zero.

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Important Questions on Rotational Mechanics

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Alpha Question Bank for Medical: Physics>Chapter 10 - Rotational Mechanics>Exercise-2>Q 29

Assertion : A solid sphere and a hollow sphere of same radius and same mass are released (at rest) from the top of a fixed inclined plane at the same time. They will reach the bottom simultaneously, if they roll with sliding.
Reason : In the situation of statement-1, the centres of both spheres have the same acceleration and they travel the same distance. Hence time taken is same.

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Alpha Question Bank for Medical: Physics>Chapter 10 - Rotational Mechanics>Exercise-2>Q 30

Assertion: A thin uniform rod is undergoing fixed axis rotation about one of its ends with variable angular acceleration. The acceleration vector of any two moving points on the rod can not be parallel at any instant of time.

Reason: For a rod undergoing fixed axis rotation, the velocity of any two moving points on the rod at different distances from the centre of rotation is different.

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Alpha Question Bank for Medical: Physics>Chapter 10 - Rotational Mechanics>Exercise-2>Q 32

Assertion: A rigid disc rolls without slipping on a fixed rough horizontal surface with uniform angular velocity. Then the acceleration of the lowest point on the disc is zero.

Reason: For a rigid disc rolling without slipping on a fixed rough horizontal surface, the velocity of the lowest point on the disc is always zero.

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Alpha Question Bank for Medical: Physics>Chapter 10 - Rotational Mechanics>Exercise-2>Q 33

Assertion: A uniform cubical block (of side $a$ ) undergoes translational motion on a smooth horizontal surface under action of horizontal force $F$ as shown. Under the given condition, the horizontal surface exerts normal reaction non-uniformly on lower surface of the block.

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Reason: For the cubical block given in statement $1$ , the horizontal force $F$ has tendency to rotate the cube about its centre in clockwise sense. Hence, the lower right edge of cube presses the horizontal surface harder in comparison to the force exerted by lower left edge of cube on horizontal surface.

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Alpha Question Bank for Medical: Physics>Chapter 10 - Rotational Mechanics>Exercise-3>Q 1

\vec{F}

be a force acting on a particle having the position vector

\vec{r}

and

\vec{τ}

be the torque of this force about the origin. Then

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Alpha Question Bank for Medical: Physics>Chapter 10 - Rotational Mechanics>Exercise-3>Q 2

Four identical thin rods, each of mass

M

and length

l

, form a square frame. The moment of inertia of this frame about an axis through the centre of the square and perpendicular to its plane is,

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Alpha Question Bank for Medical: Physics>Chapter 10 - Rotational Mechanics>Exercise-3>Q 4

The instantaneous angular position of a point on a rotating wheel is given by the equation

θ (t) = 2 t^{3} - 6 t^{2} rad

. The torque on the wheel becomes zero at time

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Alpha Question Bank for Medical: Physics>Chapter 10 - Rotational Mechanics>Exercise-3>Q 5

The moment of inertia of a thin uniform rod of mass

M

and length

L

about an axis passing through its midpoint and perpendicular to its length is

I_{0} .

Its moment of inertia about an axis passing through one of its ends and perpendicular to its length is

Assertion : If the momentum of a particle is constant, then its angular momentum will also be constant Reason : When net external force on an object is zero, then external torque on the object will also be zero.

Important Questions on Rotational Mechanics

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Assertion : If the momentum of a particle is constant, then its angular momentum will also be constant

Reason : When net external force on an object is zero, then external torque on the object will also be zero.