[3] A spring gun is set on a balcony a distance H above the ground, and fires a pellet horizontally at t=0. At that moment, a distance D from the base of the balcony, a person throws out a piece of pebble vertically upward from the ground with a speed 7. It turns out that the pellet and the pebble would collide in midair. Neglect all frictions and take H=32 m, D-25 m, and v-18 m/s. (a) What is the initial speed of the pebble? (b) What time elapsed after the pellet is fired when the collision takes place? (c) What is the velocity of the pellet just before its collision with the pebble? (Express it in terms of the unit vectors i and j).

[3] A spring gun is set on a balcony a distance H above the ground, and fires a pellet horizontally at t=0. At that moment, a distance D from the base of the balcony, a person throws out a piece of pebble vertically upward from the ground with a speed 7. It turns out that the pellet and the pebble would collide in midair. Neglect all frictions and take H=32 m, D-25 m, and v-18 m/s. (a) What is the initial speed of the pebble? (b) What time elapsed after the pellet is fired when the collision takes place? (c) What is the velocity of the pellet just before its collision with the pebble? (Express it in terms of the unit vectors i and j).