The rider tends to fall backward when a horse start suddenly. This is due to ___________ of ______________.

Answer

**Step-by-Step Solution:**

1. **Understand the Situation**: The problem describes a scenario where a rider is seated on a horse. Initially, both the horse and the rider are at rest.

2. **Identify the Motion**: When the horse starts moving suddenly in a forward direction, it accelerates from rest.

3. **Apply the Concept of Inertia**: According to Newton's First Law of Motion, an object at rest will remain at rest unless acted upon by an external force. The rider has a tendency to remain at rest due to inertia.

4. **Analyze the Effect of Inertia**: As the horse moves forward, the rider's body wants to stay in its original state of rest. This results in the rider feeling as if he is falling backward relative to the horse.

5. **Conclude the Reason**: The rider tends to fall backward when the horse starts suddenly due to the inertia of rest.

**Final Answer**: The rider tends to fall backward when a horse starts suddenly. This is due to **inertia of rest**.

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