Select the incorrect statement:

Options

A. A machine always has efficiency less than 100%
B. The mechanical advantage of a machine can be less than 1.
C. A machine can be used as a speed multiplier.
D. A machine can have mechanical advantage greater than its velocity ratio.

Answer

To solve the question of selecting the incorrect statement regarding machines, we will analyze each option step by step.

### Step 1: Analyze the first statement
**Statement:** A machine always has efficiency less than 100%.
**Analysis:** This statement is correct. Due to friction and other losses, no machine can operate at 100% efficiency. Therefore, this statement is true.

### Step 2: Analyze the second statement
**Statement:** The mechanical advantage of the machine can be less than one.
**Analysis:** This statement is also correct. Mechanical advantage (MA) is the ratio of the output force to the input force. If the output force is less than the input force, the mechanical advantage can indeed be less than one. Therefore, this statement is true.

### Step 3: Analyze the third statement
**Statement:** A machine can be used as a speed multiplier.
**Analysis:** This statement is correct. Some machines are designed to increase the speed of the output compared to the input. For example, a bicycle gear system can increase the speed of the wheels compared to the pedaling speed. Therefore, this statement is true.

### Step 4: Analyze the fourth statement
**Statement:** A machine can have mechanical advantage greater than its velocity ratio.
**Analysis:** This statement is incorrect. The efficiency of a machine is defined as the ratio of mechanical advantage (MA) to velocity ratio (VR), multiplied by 100%. According to the formula:
\[ \text{Efficiency} = \left( \frac{\text{MA}}{\text{VR}} \right) \times 100\% \]
Since efficiency cannot exceed 100%, it follows that MA cannot be greater than VR. Therefore, this statement is false.

### Conclusion
The incorrect statement is the fourth one: "A machine can have mechanical advantage greater than its velocity ratio."

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