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Finding spring constant, damping constant and Q for suspension of a car |
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| Feb27-11, 03:26 PM | #1 |
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Finding spring constant, damping constant and Q for suspension of a car
1. The problem statement, all variables and given/known data
The suspension of a car (mass= 2000kg) sags a distance of 10cm when the weight of the entire car is placed on it. Also, the amplitude of its oscillations decrease by a factor of 50% over 3 complete oscillations. a) Find the spring constant(k) b) Find the damping constant(b) c) Find the Q for the shock absorber system of one wheel assuming eah wheel supports a quarter of the weight of the car. I can do parts a and b but I don't know how to do part c 2. Relevant equations F=kx damping ratio=b/(2*sqrt(m*k) A=A0/(sqrt((1-r2)2+r2/Q2) Q = w0*m/b w0=sqrt(k/m) w=w0*sqrt(1-(b/(2M))2) where w is the frequeny of oscillation 3. The attempt at a solution a) F=kx (2000kg)*(9.81m/s2)/(0.10m) =k k=1.96*105 b) damping ratio = b/(2*sqrt(m*k)) 0.5 = b/(2*sqrt(2000kg*1.965) b= 1.98*104 c) I thought that since 1. w0=sqrt(k/m ) and 2. Q= w0*/b that the first equation can be substituted into the second equation to get 3. Q=sqrt(k/m)*m/b. I didn't get the right answer using equation 3 so I'm wondering if I used the wrong formulas. Any suggestions would be greatly appreciated.
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| car, damping ratio, oscillations, spring constant |
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