4. Two balls of the same radius are suspended from two strings. The length of each string is 0.50 m, the mass of the left ball is 0.10 kg, while the mass of the right ball is 0.30 kg. The left ball is deviated 90 to the left so that its string becomes horizontal. Then the ball is released and experiences a perfectly elastic collision with the right ball. What is the maximum height reached by the right ball? Point out the laws of physics used in your solution. (6T, 2C)