When a man walks on a horizontal surface with constant velocity, work done by

Options

A. Friction is zero
B. Contact force is zero
C. Gravity is zero
D. Man is zero

Explanation

To solve the question regarding the work done by a man walking on a horizontal surface with constant velocity, we can follow these steps:

### Step 1: Understand the Work Done Formula
The work done \( W \) by a force is given by the formula:
\[ W = F \cdot D \cdot \cos(\theta) \]
where:
- \( F \) is the force applied,
- \( D \) is the displacement,
- \( \theta \) is the angle between the force and the direction of displacement.

### Step 2: Analyze the Situation
In this scenario, the man is walking on a horizontal surface with a constant velocity. This implies that there is no net acceleration acting on him. According to Newton's first law, if an object is moving with constant velocity, the net force acting on it is zero.

### Step 3: Determine the Acceleration
Since the man is walking with constant velocity:
- Initial velocity \( u = v \)
- Final velocity \( v = u \)
- Therefore, acceleration \( a = \frac{v - u}{t} = \frac{u - u}{t} = 0 \)

### Step 4: Relate Force and Acceleration
Using Newton's second law:
\[ F = m \cdot a \]
Since the acceleration \( a = 0 \), the force \( F \) acting on the man is also zero:
\[ F = m \cdot 0 = 0 \]

### Step 5: Calculate Work Done
Now, substituting the values into the work done formula:
- Since \( F = 0 \), the work done \( W \) becomes:
\[ W = 0 \cdot D \cdot \cos(\theta) = 0 \]

### Conclusion
The work done by the man walking on a horizontal surface with constant velocity is zero.

### Final Answer
The correct answer is that the work done by the man is **zero**.

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