A simple pendulum is oscillating with angular displacement `90^(@)` For what angle with vertical the acceleration of bob direction horizontal?

Explanation

To solve the problem, we need to determine the angle at which the acceleration of the bob of a simple pendulum is directed horizontally when the pendulum is displaced at an angle of 90 degrees.

### Step-by-Step Solution:

1. **Understanding the Pendulum Motion**:
- A simple pendulum consists of a mass (bob) attached to a string that swings back and forth under the influence of gravity. When displaced from its equilibrium position, the bob experiences two types of acceleration: tangential acceleration and centripetal acceleration.

2. **Identifying the Forces**:
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