Laws of Motion MCQs for NEET — Physics Questions with Answers

In uniform circular motion on a smooth horizontal surface, the only horizontal force acting on the particle towards the center is the tension in the string. This tension provides the necessary centripetal force. Therefore, the net force directed towards the center is T. This directly corresponds to problem 4.4 in the provided context.

First, calculate the acceleration: $a = (v - u) / t = (3.5 m/s - 2.0 m/s) / 25 s = 1.5 m/s / 25 s = 0.06 m/s^2$. Then, use Newton's Second Law: $F = ma = (3.0 kg)(0.06 m/s^2) = 0.18 N$. This aligns with problem 4.6 in the provided context.

According to the NCERT text, 'The total momentum of an isolated system of interacting particles is conserved.' This means that in the absence of external forces, the total momentum of the system remains unchanged.

The NCERT text states: 'Since $F_{AB} = - F_{BA}$ by the third law, $(p_A' - p_A) = - (p_B' - p_B)$ i.e. $p_A' + p_B' = p_A + p_B$'. This shows that the total final momentum of the isolated system equals its initial momentum.

The NCERT text explicitly states regarding the equality of total initial and final momentum: 'Notice that this is true whether the collision is elastic or inelastic.'

The NCERT text mentions that 'In an inelastic collision of two bodies, the quantities which do not change after the collision are the total linear momentum/total energy of the system of two bodies'. It also states 'In an inelastic collision, the final kinetic energy is always less than the initial kinetic energy of the system.' Therefore, total kinetic energy is not conserved in an inelastic collision.

The NCERT states: 'Thus if $p_b$ is the momentum of the bullet after firing and $p_g$ is the recoil momentum of the gun, $p_g = -p_b$ i.e. $p_b + p_g = 0$. That is, the total momentum of the (bullet + gun) system is conserved.' This implies that the initial total momentum (zero) equals the final total momentum.

The NCERT text explains: 'In an isolated system (i.e. a system with no external force), mutual forces between pairs of particles in the system can cause momentum change in individual particles, but since the mutual forces for each pair are equal and opposite, the momentum changes cancel in pairs and the total momentum remains unchanged.'

The NCERT clearly states: 'The total momentum of an isolated system of particles is conserved.' An isolated system is one with no external force.

The NCERT states under 'POINTS TO PONDER': 'During a collision: (a) the total linear momentum is conserved at each instant of the collision; (b) the kinetic energy conservation (even if the collision is elastic) applies after the collision is over and does not hold at every instant of the collision.'