请帮我看一个碰撞的问题，谢谢

andyliu22708

玩冰上滚石游戏时，一个半径为0.3米平的圆盘以0。75米/秒的速度扔向目标。在玩的时候，由于其他人已经扔不少圆盘， 所以在目标的2半径范围内，布满了密度为1个/平方米的圆盘。（直到撞到其他圆盘之前，假设速度恒定），被扔出的圆盘在每秒钟撞到其中一个圆盘的可能性是多少？
这是翻译过来的，明天要交。帮帮忙，谢谢。
原文：
The game of "curling"is somewhat similar to lawn bowls , but is played on a flat sheet of ice. A flat circular disk, with diameter 0.3 m, is thrown so it slides across the ice towards a target, there may be disks previously thrown by other competitors surrounding the target. The sliding disk may collide with these stationary disks as it approaches the target.
Suppose that disks are randomly placed on the ice surface within a 2m radius of the target at an average of 1/m2 of ice surface. A disk is projected roughly towards the target at a speed of 0.75 m/s (you may assume the velocity remains constant until a collision occurs). What is the probability that the sliding disk will hit one of the randomly placed disks within one second of crossing the 2 m radius from the target. Note: If the probability were 50% we would say the collision rate of the disk was 0.5 collisions/second.