Which of the following statements is incorrect?

Options

A. Kinetic energy may be zero, positive or negative
B. Power, energy and work are all scalars
C. Potential energy may be zero, positive or negative
D. Ballistic pendulum is a device for measuring the speed of bullets

Explanation

To determine which statement is incorrect among the given options, we will analyze each statement one by one.

### Step 1: Analyze Kinetic Energy
- Kinetic energy (KE) is given by the formula:
\[ KE = \frac{1}{2} mv^2 \]
where \(m\) is mass and \(v\) is velocity.
- Since \(v^2\) (the square of velocity) is always non-negative (i.e., it can be zero or positive), it follows that kinetic energy cannot be negative. Therefore, the statement "Kinetic energy may be zero, positive or negative" is incorrect.

### Step 2: Analyze Power, Energy, and Work
- Power, energy, and work are all scalar quantities. Scalars have magnitude but no direction.
- Thus, the statement "Power, energy and work are all scalars" is correct.

### Step 3: Analyze Potential Energy
- Potential energy (PE) can be zero, positive, or negative depending on the reference point chosen.
- For example, gravitational potential energy can be negative if the object is below a chosen reference level. Therefore, the statement "Potential energy may be zero, positive or negative" is correct.

### Step 4: Analyze the Ballistic Pendulum
- A ballistic pendulum is indeed a device used to measure the speed of bullets by capturing the bullet in a pendulum and measuring the resulting motion.
- Therefore, the statement "Ballistic pendulum is a device for measuring the speed of bullets" is correct.

### Conclusion
After analyzing all statements:
- The incorrect statement is the first one: "Kinetic energy may be zero, positive or negative."

### Final Answer
The incorrect statement is: **Kinetic energy may be zero, positive or negative.**

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