Concept explainers
Rod AB is rigidly attached to the frame of a motor running at a constant speed. When a collar of mass m is placed on the spring, it is observed to vibrate with an amplitude of 15 mm. When two collars, each of mass m, are placed on the spring, the amplitude is observed to be 18 mm. What amplitude of vibration should be expected when three collars, each of mass m, are placed on the spring? (Obtain two answers.)
Fig. P19.112
Find the amplitude of vibration
Answer to Problem 19.112P
The amplitude of vibration
Explanation of Solution
Given information:
The amplitude of the one collar
The amplitude of the two collars
Calculation:
The expression for the natural frequency
Here,
The expression for the amplitude of forced vibration
Here,
Consider only one collar is placed.
Calculate the natural frequency when only one collar is placed using the relation:
Here,
Substitute
Here,
Substitute 15 mm for
Consider two collars are placed.
Find the natural frequency:
Substitute 2m for m in equation (1).
Here,
Substitute
Multiply both sides by
Substitute
Here,
Substitute
Consider three collars are placed.
Find the natural frequency:
Substitute 3m for m in equation (1).
Here,
Substitute
Multiply both sides by
Substitute
Here,
Substitute
The amplitude given in equation (8), can be in-phase with or out-of-phase with the periodic force.
In-phase motion:
Substitute 18 mm for
Divide equation (13) by equation (4).
Substitute
Substitute 12.855 mm for
Out-of-phase motion:
Substitute -18 mm for
Divide equation (14) by equation (4).
Substitute 0.647 for
Substitute 5.295 mm for
Therefore, the amplitude of vibration
Want to see more full solutions like this?
Chapter 19 Solutions
Vector Mechanics for Engineers: Statics and Dynamics
- An 8-kg uniform disk of radius 200 mm is welded to a vertical shaft with a fixed end at B. The disk rotates through an angle of 3° when a static couple of magnitude 50N.m is applied to it. If the disk is acted upon by a periodic torsional couple of magnitude Tm=60N.m. determine the range of values of vf for which the amplitude of the vibration is less than the angle of rotation caused by a static couple of magnitude Tm.arrow_forwardA slender 10-kg bar AB with a length of l = 0.6 m is connected to two collars of negligible weight. Collar A is attached to a spring with a constant of k = 1.5 kN/m and can slide on a horizontal rod, while collar B can slide freely on a vertical rod. Knowing that the system is in equilibrium when bar AB is vertical and that collar A is given a small displacement and released, determine the period of the resulting vibrations.arrow_forwardA 400-kg motor supported by four springs, each of constant 150 kN/m, and a dashpot of constant c = 6500 N·s/m is constrained to move vertically. Knowing that the unbalance of the rotor is equivalent to a 23-g mass located at a distance of 100 mm from the axis of rotation, determine for a speed of 800 rpm (a ) the amplitude of the fluctuating force transmitted to the foundation, (b ) the amplitude of the vertical motion of the motor.arrow_forward
- A motor of mass M is supported by springs with an equivalent spring constant k The unbalance of its rotor is equivalent to a mass m located at a distance r from the axis of rotation. Show that when the angular velocity of the motor is wf, the amplitude of the motion of the motor is wherearrow_forwardA vibrometer used to measure the amplitude of vibrations consists essentially of a box containing a mass-spring system with a known natural frequency of 120 Hz. The box is rigidly attached to a surface that is moving according to the equation y= δm sin wf t. If the amplitude zm of the motion of the mass relative to the box is used as a measure of the amplitude δm of the vibration of the surface, determine (a) the percent error when the frequency of the vibration is 600 Hz,(b) the frequency at which the error is zero.arrow_forwardVibration When suspended from a helical spring, a load of 91 kg is found to vibrate vertically with a periodic time of 0.75 s. Determine, for an amplitude of 51 mm : (a) the angular velocity of the generating vector; (b) the maximum acceleration; (c) the acceleration when the displacement is 127 mm; (d) the stiffness of the spring; (e) the static deflection in the spring; (f) the maximum force in the spring (122 N).arrow_forward
- A machine of mass 75 kg is mounted on springs and is fitted with a dashpot to damp out vibrations. There are three springs each of stiffness 10 N/mm and it is found that the amplitude of vibration diminishes from 38.4 mm to 6.4 mm in two complete oscillations. Assuming that the damping force varies as the velocity, determine : 1. the resistance of the dash-pot at unit velocity ; 2. the ratio of the frequency of the damped vibration to the frequency of the undamped vibration ; and 3. the periodic time of the damped vibration.arrow_forwardA uniform disk with radius r and mass m can roll without slipping on a cylindrical surface and is attached to bar ABC with a length L and negligible mass. The bar is attached at point A to a spring with a constant k and can rotate freely about point B in the vertical plane. Knowing that end A is given a small displacement and released, determine the frequency of the resulting vibration in terms of m, L,K and g.arrow_forwardA 360-lb motor is supported by springs of total constant 12.5 kips/ft. The unbalance of the rotor is equivalent to a 0.9-oz weight located 7.5 in. from the axis of rotation. Determine the range of speeds of the motor for which the amplitude of the fluctuating force exerted on the foundation is less than 5 lb.arrow_forward
- Elements Of ElectromagneticsMechanical EngineeringISBN:9780190698614Author:Sadiku, Matthew N. O.Publisher:Oxford University PressMechanics of Materials (10th Edition)Mechanical EngineeringISBN:9780134319650Author:Russell C. HibbelerPublisher:PEARSONThermodynamics: An Engineering ApproachMechanical EngineeringISBN:9781259822674Author:Yunus A. Cengel Dr., Michael A. BolesPublisher:McGraw-Hill Education
- Control Systems EngineeringMechanical EngineeringISBN:9781118170519Author:Norman S. NisePublisher:WILEYMechanics of Materials (MindTap Course List)Mechanical EngineeringISBN:9781337093347Author:Barry J. Goodno, James M. GerePublisher:Cengage LearningEngineering Mechanics: StaticsMechanical EngineeringISBN:9781118807330Author:James L. Meriam, L. G. Kraige, J. N. BoltonPublisher:WILEY