- #1
TheSwedeAtLarge
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Hi all!
I am currently working on an assignment for my dynamics course in which we need to create our own "real world" problems. I chose to do a problem which would solve the time at which the string of a lanyard would break when it is swung in a circle. My problem is with my end numbers. They seem very unreasonable but I am not sure if it is due to a calculation error, a dynamics error, or if it is simply the nature of the problem. I estimated the mass of the keys. The maximum load is from this website: http://www.engineeringtoolbox.com/polyester-rope-strength-d_1514.html
The torque of the motor is an arbitrary number that I chose.
Any feedback would be greatly appreciated.
1. Homework Statement
A motor is set up to spin a lanyard from rest with keys attached with a torque of 5 Nm. The polyester lanyard is 50 centimeters long with a diameter of 6 mm, assume it is massless. The keys have a mass m = 100 grams. The maximum load of polyester rope is Tmax = 3400 N. At what time will the rod break and after how many revolutions? Gravity acts in the -j direction. Neglect bending stresses and air resistance.
Schematic: http://imgur.com/V6mSuuD
FBD/KD: http://imgur.com/AQShsEv
F=ma
w = w0 + at
Find Angular Velocity[/B]
Sum forces in the y-direction and solve for w
Tmax – mg = mrw2
w = 260.7 rad/s
Find Angular Acceleration
Sum moments about the origin
M = (mra) * (r)
a=M/mr^2
a = 200 rad/s2
Use kinematics to find the time to break
w = w0 + at
260.7 rad/s = 200 rad/s2 * t
t = 1.3 s
I am currently working on an assignment for my dynamics course in which we need to create our own "real world" problems. I chose to do a problem which would solve the time at which the string of a lanyard would break when it is swung in a circle. My problem is with my end numbers. They seem very unreasonable but I am not sure if it is due to a calculation error, a dynamics error, or if it is simply the nature of the problem. I estimated the mass of the keys. The maximum load is from this website: http://www.engineeringtoolbox.com/polyester-rope-strength-d_1514.html
The torque of the motor is an arbitrary number that I chose.
Any feedback would be greatly appreciated.
1. Homework Statement
A motor is set up to spin a lanyard from rest with keys attached with a torque of 5 Nm. The polyester lanyard is 50 centimeters long with a diameter of 6 mm, assume it is massless. The keys have a mass m = 100 grams. The maximum load of polyester rope is Tmax = 3400 N. At what time will the rod break and after how many revolutions? Gravity acts in the -j direction. Neglect bending stresses and air resistance.
Schematic: http://imgur.com/V6mSuuD
FBD/KD: http://imgur.com/AQShsEv
Homework Equations
F=ma
w = w0 + at
The Attempt at a Solution
Find Angular Velocity[/B]
Sum forces in the y-direction and solve for w
Tmax – mg = mrw2
w = 260.7 rad/s
Find Angular Acceleration
Sum moments about the origin
M = (mra) * (r)
a=M/mr^2
a = 200 rad/s2
Use kinematics to find the time to break
w = w0 + at
260.7 rad/s = 200 rad/s2 * t
t = 1.3 s