Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Car's vibration after being compressed, and released on springs

  1. Oct 29, 2008 #1
    1. When seven people whose average mass is 83 kg sit down in a car they find that the car drops down 0.87cm lower on its springs. Then they get out of the car and bounce it up and down. The acceleration of gravity os 9.8m/s^2.
    What is the frequency of the car's vibration if its mass (empty) is 1100kg? Answer in units of Hz.

    2. f= 1/2pi (sqrt k/m)

    k=F/x= mg/x

    m1f1^2 = m2f2^2

    3. First I solved for k: k= mg/ x = 1183 kg (9.8) / .0087m= 1332574.713 N/m

    Then I solved for f1= 1/2pi (sqrt k/m)= 1/2pi (sqrt (1332574.713/ 1183kg)= 5.34 Hz

    Now, when I tried to use these numbers in m1f1^2= m2f2^2 and solve for f2
    1183kg(5.34)^2 = 1100kg (f2)^2
    f2= 5.539 Hz
    But this is wrong. Help!
  2. jcsd
  3. Oct 29, 2008 #2

    F=kx > G=kx > (83*7)g = k *.0087

    f1= 1/2pi (sqrt k/m)= 1/2pi(sqrt(k/1100))
  4. Oct 29, 2008 #3
    Thank you! I missed the 83 kg * 7 people.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook