On a railway curve, the outside rail is laid higher than the inside one so that resultant force exerted on the wheels of the rail car by the tops of the rails will

Options

A. equilibrate the centripetal force
B. be vertical
C. be decreased
D. have a horizontal inward component

Explanation

To solve the question, we need to understand the concept of banking of curves in circular motion, particularly in the context of a railway curve. The outside rail being higher than the inside rail is a design feature that helps in providing the necessary centripetal force for a train moving along a curved path.

### Step-by-Step Solution:

1. **Understanding the Setup**:
- When a train moves along a curved track, it experiences a centripetal force that keeps it moving in a circular path. This force is directed towards the center of the curve.
- The banking of the track means that the outside rail is elevated compared to the inside rail.

2. **Forces Acting on the Train**:
- The forces acting on the train include the gravitational force (weight of the train) acting downwards and the normal force exerted by the rails on the wheels of the train.
- The normal force will have two components: a vertical component (which balances the weight of the train) and a horizontal component (which provides the necessary centripetal force).

3. **Analyzing the Normal Force**:
- When the track is banked, the normal force is not vertical but acts at an angle. This angle allows the normal force to have a horizontal component that points towards the center of the curve.
- The horizontal component of the normal force (let's denote it as \( N_H \)) provides the centripetal force required for the train to navigate the curve.

4. **Centripetal Force Requirement**:
- The required centripetal force \( F_c \) for an object moving in a circular path is given by the formula:
\[ F_c = \frac{mv^2}{R} \]
where \( m \) is the mass of the train, \( v \) is its velocity, and \( R \) is the radius of the curve.

5. **Conclusion**:
- The banking of the track ensures that the resultant force exerted on the wheels of the rail car has a horizontal inward component, which is essential for providing the centripetal force necessary for the train to maintain its curved path.
- Therefore, the correct answer to the question is that the resultant force exerted on the wheels of the rail car by the tops of the rails will have a horizontal inward component.

### Final Answer:
The resultant force exerted on the wheels of the rail car by the tops of the rails will have a horizontal inward component.