A rigid body is rotating about an axis. The best way to stop it is applying

Options

A. pressure at the turning point.
B. upward force at the turning point.
C. downward force at the free end.
D. torque in opposite direction.

Answer

To solve the problem of stopping a rigid body that is rotating about an axis, we need to understand the concept of torque and how it affects rotational motion. Here’s a step-by-step solution:

### Step 1: Understand the Motion of the Rigid Body
The rigid body is rotating about a fixed axis. This means that all points in the body are moving in circular paths around that axis.

**Hint:** Identify the direction of rotation to understand how to counteract it.

### Step 2: Identify the Forces Acting on the Body
When a rigid body is rotating, it experiences angular momentum. To stop the rotation, we need to apply a force that can change this angular momentum.

**Hint:** Consider how forces can create torque, which is necessary to change the rotational motion.

### Step 3: Apply Torque in the Opposite Direction
To effectively stop the rotation, we need to apply a torque in the opposite direction of the rotation. This means if the body is rotating clockwise, we should apply a torque that rotates it counterclockwise.

**Hint:** Remember that torque is the product of force and the distance from the axis of rotation.

### Step 4: Determine the Best Application of Force
Applying a force at the turning point or free end may not effectively stop the rotation because it does not create sufficient torque to counteract the existing rotational motion. Instead, applying a torque directly opposite to the direction of rotation is the most effective method.

**Hint:** Think about how the application of torque can be maximized by considering the point of application and the direction of the force.

### Step 5: Conclusion
The best way to stop a rigid body that is rotating about an axis is to apply torque in the opposite direction of its rotation.

**Final Answer:** The best way to stop it is by applying torque in the opposite direction.