Physics MCQs for NEET — Practice Questions with Answers

The NCERT text provides the determinant form: '$\vec{a} \times \vec{b} = |\begin{smallmatrix} \hat{i} & \hat{j} & \hat{k} \\ a_x & a_y & a_z \\ b_x & b_y & b_z \end{smallmatrix}|$.'

The NCERT text states: 'Thus, the time rate of change of the angular momentum of a particle is equal to the torque acting on it. This is the rotational analogue of the equation $\vec{F} = d\vec{p}/dt...$'

The NCERT text defines angular momentum: '$\vec{l} = \vec{r} \times \vec{p}$.'

The NCERT text mentions: 'The linear velocity of the particle at P is $\vec{v} = \vec{\omega} \times \vec{r}$'.

The NCERT text states: 'For rotation about a fixed axis, the angular velocity vector lies along the axis of rotation, and points out in the direction in which a right handed screw would advance...'

The magnitude of the vector product is $ab\sin\theta$. If two vectors are parallel, $\theta = 0^\circ$ or $\theta = 180^\circ$. In both cases, $\sin\theta = 0$. Therefore, the magnitude of the vector product is zero, making it a zero vector. The text states: 'd(r $\times$ p)/dt = r $\times$ dp/dt + dr/dt $\times$ p. Now, the velocity of the particle is v = dr/dt and p = m v. Because of this d(r $\times$ p)/dt = r $\times$ dp/dt + v $\times$ mv. The term v $\times$ mv is zero as the vector product of two parallel vectors vanishes.'

According to the NCERT text, 'To summarise, if the net external force is zero, a body at rest continues to remain at rest and a body in motion continues to move with a uniform velocity.' This accurately describes Newton's First Law, emphasizing uniform velocity, not constant acceleration, in the absence of a net external force.

The NCERT text states: 'This property of the body is called inertia. Inertia means ‘resistance to change’.' Therefore, inertia is the correct term for this property.

The text states that Newton's second law is consistent with the First Law ($F = 0$ implies $a = 0$). This means if the net external force is zero, the acceleration (rate of change of velocity) is also zero. This aligns with the concept of inertia, where a body maintains its state of motion (either rest or uniform velocity).

The NCERT text mentions: 'Galileo thus, arrived at a new insight on motion that had eluded Aristotle and those who followed him. The state of rest and the state of uniform linear motion (motion with constant velocity) are equivalent. In both cases, there is no net force acting on the body.'