A butterfly rests on a leaf floating on the surface of a pond. The butterfly then starts moving to the tip of the leaf at a speed of 5 cm s -1 relative to the water. The leaf，in accordance with the principle of conservation of momentum，moves at 3 cm s -1 relative to the water in the opposite direction. If the mass of the leaf is 8g，determine the mass of the butterfly.

Greg drew a diagram to compare two of the fundamental forces. which labels belong in the areas marked x, y and z? gravitational force electromagnetic force x. attractive y repulsive z: infinite range x: infinite range y attractive z. repulsive x. always attractive y: infinite range z: attractive or repulsive x. attractive or repulsive y infinite range z: always attractive