Physics
Physics
Problem
Two ice skaters initially at rest push against each other on frictionless ice. Which statement best explains why their total momentum after the push is zero (assuming negligible external forces)? a) Because kinetic energy is conserved in their interaction, the total momentum must remain zero. b) The forces they exert on each other are equal in magnitude and opposite in direction, so their impulses cancel within the system. c) The action–reaction forces between the skaters cancel out, so there is no net force and they cannot accelerate; therefore their momenta stay zero. d) Each skater has the same mass, so their velocities are equal and opposite, giving zero total momentum.Intuitive explanation
This is about conservation of momentum and understanding action-reaction pairs. When the skaters push against each other, they exert equal and opposite forces on one another—Newton's third law in action. Since they start at rest (zero total momentum) and no external forces act on the system, momentum must be conserved: whatever momentum one skater gains in one direction, the other must gain equally in the opposite direction, keeping the total at zero.
Intuitive explanation
This is about conservation of momentum and understanding action-reaction pairs. When the skaters push against each other, they exert equal and opposite forces on one another—Newton's third law in action. Since they start at rest (zero total momentum) and no external forces act on the system, momentum must be conserved: whatever momentum one skater gains in one direction, the other must gain equally in the opposite direction, keeping the total at zero.