Which of the following statements is correct?

Options

A. Motion of soldiers on march past is a periodic motion.
B. Motion of a train along a curved track on hills is an example of curvilinear motion.
C. Every periodic motion is also an oscillatory motion.
D. Hockey player running after a ball is a combined motion.

Explanation

To determine which statement is correct, let's analyze each statement provided in the question:

1. **Motion of soldier on march past is periodic motion.**
- **Explanation:** Periodic motion is defined as motion that repeats itself after equal intervals of time. In the case of soldiers marching, while they may march in a synchronized manner, their motion does not repeat in a regular cycle after equal intervals. Therefore, this statement is **incorrect**.

2. **Motion of a train along a curved track on hills is an example of curvilinear motion.**
- **Explanation:** Curvilinear motion refers to motion that occurs along a curved path. A train moving along a curved track, especially in hilly areas, clearly fits this definition as it does not move in a straight line but rather follows a curved trajectory. Therefore, this statement is **correct**.

3. **Each periodic motion is also an oscillatory motion.**
- **Explanation:** While all oscillatory motions are periodic (they repeat in cycles), not all periodic motions are oscillatory. For example, the motion of a clock's hands is periodic but not oscillatory. Therefore, this statement is **incorrect**.

4. **Hockey player running after a ball is combined motion.**
- **Explanation:** Combined motion refers to the motion that involves more than one type of motion, such as linear and rotational motion. While a hockey player may exhibit combined motion, this statement does not provide a definitive answer to the question of correctness compared to the other statements.

Based on the analysis, the correct statement is:
**Motion of a train along a curved track on hills is an example of curvilinear motion.**

### Steps:
1. Identify the definitions of periodic and curvilinear motion.
2. Analyze the motion of soldiers on march past.
3. Analyze the motion of a train along a curved track.
4. Evaluate the statement about periodic and oscillatory motion.
5. Assess the statement about the hockey player's motion.
6. Conclude which statement is correct.