JEE (Main) Physics - Law of Conservation of Linear Momentum and Equilibrium of Concurrent Forces: MCQs (16-30)

16. Which of the following is true for a system where the law of conservation of momentum is valid?
    • a) The momentum is always zero.
    • b) The total momentum is conserved if no external forces act on the system.
    • c) The momentum is conserved only in elastic collisions.
    • d) The momentum of individual objects is conserved.
    Answer: b) The total momentum is conserved if no external forces act on the system.
17. Which of the following is true for the total momentum of a system before and after an inelastic collision?
    • a) It increases.
    • b) It remains constant.
    • c) It decreases.
    • d) It becomes zero.
    Answer: b) It remains constant.
18. In an isolated system, if two objects collide and stick together, which of the following quantities are conserved?
    • a) Momentum only.
    • b) Kinetic energy only.
    • c) Momentum and energy.
    • d) Neither momentum nor energy.
    Answer: a) Momentum only.
19. The net external force acting on a system is zero. What happens to the momentum of the system?
    • a) The momentum remains constant.
    • b) The momentum changes with time.
    • c) The momentum becomes zero.
    • d) The momentum increases.
    Answer: a) The momentum remains constant.
20. Which of the following does not change during a perfectly elastic collision?
    • a) Kinetic energy
    • b) Momentum
    • c) Speed
    • d) Velocity
    Answer: a) Kinetic energy
21. In an elastic collision, what remains unchanged?
    • a) Total energy
    • b) Momentum
    • c) Velocity
    • d) Kinetic energy
    Answer: d) Kinetic energy
22. If two objects have equal but opposite velocities, what will be the total momentum of the system?
    • a) Zero
    • b) Maximum
    • c) Minimum
    • d) Infinite
    Answer: a) Zero
23. For a body to be in equilibrium, which of the following must be true?
    • a) The sum of all forces acting on it must be zero.
    • b) The net torque must be non-zero.
    • c) The body should be in motion.
    • d) There should be a net external force.
    Answer: a) The sum of all forces acting on it must be zero.
24. If the resultant of all the forces acting on a body is zero, the body will:
    • a) Start moving.
    • b) Stay at rest.
    • c) Continue moving in a straight line at constant speed.
    • d) None of the above.
    Answer: c) Continue moving in a straight line at constant speed.
25. Which of the following is true for a system of forces in equilibrium?
    • a) The sum of the forces is zero.
    • b) The sum of the forces is non-zero.
    • c) The body moves with constant speed.
    • d) The velocity is non-zero.
    Answer: a) The sum of the forces is zero.
26. For a body in equilibrium under the action of three concurrent forces, which condition must hold true?
    • a) The sum of the three forces must be zero.
    • b) The net torque must be non-zero.
    • c) The forces must be coplanar and in the same line.
    • d) The forces must be parallel.
    Answer: a) The sum of the three forces must be zero.
27. In the case of equilibrium of a body under three forces, which of the following must happen?
    • a) The forces must act at the same point.
    • b) The forces must be equal in magnitude.
    • c) The forces must be non-parallel.
    • d) The forces must be in equilibrium at their intersection.
    Answer: a) The forces must act at the same point.
28. Which of the following conditions must be true for equilibrium of a body under three concurrent forces?
    • a) The forces must be collinear.
    • b) The sum of the forces must be zero.
    • c) The forces must be perpendicular to each other.
    • d) The body must remain stationary.
    Answer: b) The sum of the forces must be zero.
29. When three forces act on a body in equilibrium, the body will not rotate if:
    • a) The sum of the torques about any point is zero.
    • b) The forces are applied at the same point.
    • c) The forces form an equilateral triangle.
    • d) The forces form a right-angle triangle.
    Answer: a) The sum of the torques about any point is zero.
30. Which of the following is a necessary condition for a system of forces to be in equilibrium?
    • a) The net force must be non-zero.
    • b) The sum of all torques must be zero.
    • c) The object must be stationary.
    • d) The forces must be applied at the same point.
    Answer: b) The sum of all torques must be zero.

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