If a molecule in a gas container hits a horizontal wall and rebounds with the same speed but an angle of 30° with the normal, is momentum conserved in the collision at the wall, considering a single molecule and the wall?
The question asks 'Is momentum conserved in the collision?' If we consider just the molecule, its momentum changes in direction, so its momentum isn't conserved. However, for the system of the molecule and the wall, momentum is conserved. The NCERT implicitly refers to the 'system' being conserved. When a molecule hits a wall and rebounds, the wall experiences an impulse equal and opposite to the impulse on the molecule, ensuring conservation of momentum for the molecule-wall system. The text for the example problem 5.14 doesn't explicitly state the answer for the question posed within the problem statement, but general principle implies system momentum conservation.