Problem
Problem
Two identical balls are shot upward one after another at an interval of 2s along the same vertical line with same initial velocity of . The height at which the balls collide is a. 50 m b. 75 m c. 100 m d. 125 mIntuitive explanation
This is a relative motion problem disguised as a collision puzzle. The key insight is that instead of tracking both balls in the ground frame, imagine sitting on the first ball—from that perspective, the second ball appears to chase it with a specific relative velocity. Since both balls experience the same gravity, their relative acceleration is zero, making the second ball's motion relative to the first purely kinematic. Find when and where they meet by using the 2-second head start and matching their positions.
Intuitive explanation
This is a relative motion problem disguised as a collision puzzle. The key insight is that instead of tracking both balls in the ground frame, imagine sitting on the first ball—from that perspective, the second ball appears to chase it with a specific relative velocity. Since both balls experience the same gravity, their relative acceleration is zero, making the second ball's motion relative to the first purely kinematic. Find when and where they meet by using the 2-second head start and matching their positions.