Chapter 3 Principle 3

Example 14.4 known: the side length of a uniform square flat is fixed, fixed, regardless of the weight of a pole. (Figure 14.10)

Fig. 14.10 ()

Q: What is the force and angular acceleration of the two poles when the rope is cut off?

Solution: 1. Study object: Square flat

2. analyze the stress (,,)

1. Analysis of motion, virtual and inertial force

Figure 14.10 (B) Figure 14.10 (c)

Flat composing line translation

4. Application of Dynamic and Static Methods

Simultaneous (a) (B:

,

Substitute, get

,,

The angle acceleration of the rod is

Example 14.5 known 5 known: as shown in Figure 14.11, a right-angle rod is welded by a homogeneous rod OA and AB, And it rotates around the lead direct shaft O in a smooth horizontal plane. Set the quality of the rod AB to 2 m.

Figure 14.11 (a) Figure 14.11 (B)

Q: What is the internal force of Solder Joint A when the angular acceleration of an instantaneous rod is used?

Solution: 1. Study object: Rod

1. analyze the stress (,,)

3. Analysis of motion, virtual and inertial force

,

4. Application of Dynamic and Static Methods

The answer is ,,

For example, 14.6 it is known that uniform 6 is known: the uniform cylindrical is in the lead plane, the radius is R, and the weight is P, (Figure 14.12), and the angle acceleration of the moment B is removed? Binding Force of Point?

Fig. 14.12 ()

Solution: 1. Study object: cylindrical

2. analyze the stress (,,)

3. Analysis of motion, virtual and inertial force

,

Fig. 14.12 (B)

4. Application of Dynamic and Static Methods

Where ,,

Solution,

Example 14.7 known: In Figure 14.13, wheel C is a Homogeneous Disc with a radius of R and a mass of M. When the rod is purely rolled, the wheel c is static, the angle between the OA rod and the lead line is not counted.

Fig. 14.13 ()

Q: How long is the center C moving from S ,? Weld o binding force?

Solution: 1. Research round (,,,,)

Fig. 14.13 (B)

,

The answer is ,,

2. Study oa pole (,,,)

Fig. 14.13 (c)

The answer is ,,

Example 14.8 known: homogeneous rod AB, weight M, length, suspended with a soft rope ad, Be, 14.14.

Q: When the be rope is cut off, is the acceleration of the AB pole angle and the tension of the AD rope?

Solution: 1. Study: Rod

2. analyze the stress (,)

3. Analysis of motion, virtual and inertial force

When the be rope is cut off, the AB rod performs a plane movement.

,,

Kinematics relationship:

[] Y: (3)

Simultaneous expressions (1), (2), and (3)

,,

Example 14.9 known: as shown in Figure 14.14, the weight of the homogeneous drum wheel installed on the cantilever beam is P, the radius is R, and the force-even moment is m, and the weight of C is P2, set, the beam weight is not counted.

The acceleration of heavy lifting and the binding force of fixed end

Figure 14.14 (a) Figure 14.14 (B)

Solution: 1. Study object: Whole

Fig. 14.14 (c)

2. Use the kinetic energy theorem to find the rising acceleration of things c.

If the Rising Speed of the C object is V, the drum wheel's angular velocity is. When the heavy object rises, the drum wheel turns,

,

Simplified

Divide the two sides of the above formula

Because

3. Use static and dynamic methods to determine the binding force of Point

Inertia Force,