第二小题讲解一下---**Extraction Content:**
**Title:** 典型例 (2024·福建·高考真题)
**Problem Description:**
如图，直角坐标系 xOy 中，第 I 象限内存在垂直纸面向外的匀强磁场。第 II、III 象限中有两平行板电容器 C₁、C₂，其中 C₁ 垂直 x 轴放置，极板与 x 轴相交处存在小孔 M、N；C₂ 垂直 y 轴放置，上、下极板右端分别紧贴 y 轴上的 P、O 点。一带电粒子从 M 静止释放，经电场直线加速后从 N 射出，紧贴 C₂ 下极板进入 C₂，而后从 P 进入第 I 象限；经磁场偏转后恰好垂直 x 轴离开，运动轨迹如图中虚线所示。已知粒子质量为 m、带电量为 q，O、P 间距离为 d，C₁、C₂ 的板间电压大小均为 U，板间电场视为匀强电场，不计重力，忽略边缘效应。求：
**Diagram Description:**
* **Type:** Physics setup diagram showing particle motion in electric and magnetic fields.
* **Coordinate System:** A Cartesian coordinate system with x and y axes intersecting at O. The y-axis is vertical, and the x-axis is horizontal. The origin is labeled O.
* **Regions:** The diagram shows the four quadrants of the xOy plane. The problem statement specifies regions:
* Quadrant I (x > 0, y > 0): Contains a uniform magnetic field pointing out of the page. A grid of dots is shown in this region.
* Quadrants II and III (x < 0): Contain parallel plate capacitors C₁ and C₂.
* **Capacitors:**
* C₁: Parallel plates oriented vertically (perpendicular to the x-axis). Located in Quadrant III and potentially II. It has small holes labeled M and N where it intersects the x-axis. M is to the left of N.
* C₂: Parallel plates oriented horizontally (perpendicular to the y-axis). Located in Quadrant II. The right ends of the plates are along the y-axis at points P (upper plate) and O (lower plate).
* **Points:** M and N on the x-axis (left of O), P on the y-axis (above O), O at the origin (0,0).
* **Particle Trajectory:** Shown as a dashed blue line. The particle starts at M, moves to N (straight line, accelerated), enters C₂ at N, follows a curved path through C₂ (close to the bottom plate), enters Quadrant I at P, follows a curved path (part of a circle) in Quadrant I, and exits Quadrant I perpendicular to the x-axis.
* **Labels and Annotations:** C₁, C₂, M, N, P, O, x, y are labeled. The dashed line represents the particle's trajectory. The grid of dots in Quadrant I indicates the magnetic field region.
**Questions:**
(1) 粒子经过 N 时的速度大小；
(2) 粒子经过 P 时速度方向与 y 轴正向的夹角；