A particle of mass m is projected with velocity v at an angle `theta` with the horizontal. Find its angular momentum about the point of projection when it is at the highest point of its trajectory.

Explanation

To find the angular momentum of a particle of mass \( m \) projected with velocity \( v \) at an angle \( \theta \) with the horizontal at the highest point of its trajectory, we can follow these steps:

### Step 1: Understand the motion of the particle
When a particle is projected at an angle \( \theta \), it follows a parabolic trajectory. At the highest point of this trajectory, the vertical component of the velocity becomes zero, and only the horizontal component remains.

### Step 2: Determine the horizontal component of the velocity
The horizontal component of the initial velocity \( v \) is given by:
\[
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