未解决

高一三道物理题目..十万火急...在线等...
(1) Two pieces of string, each of length 1 m, are fixed to a common point A; their masses are 3 kg and 1 kg respectively. The 3 kg mass is pulled aside until this string makes an angle of 60° with vertical. It is then released. If the masses stick together on collision, find the height to which they rise.
(2) AB is a smooth circular track of radius R and centre O; BC is a smooth horizontal surface. The ball at A rolls down along AB and collide with a stationary ball at B. They stick together and move off to collide with a third ball at C. If these three balls stick together after their collisions, what is their common final velocity?
(4) A 0.75 kg bullet is fired in a horizontal direction through block X and becomes embedded in block Y. The bullet causes X and Y to start moving with velocities
15 m/s and 12 m/s respectively. Determine:
(a) the initial velocity v0 of the bullet.
(b) the velocity of the bullet as it travels from block X to block Y.
只要列式就可以了。。这部分学得不是很好。。所以很久也没做出来。。
哪位大人能帮帮忙吗，感激不尽。。