- #1
Destroxia
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Homework Statement
An automobile with a mass of 1000 kg, including passengers, settles 1.0 cm closer to the road for every additional 100 kg of passengers. It is driven with a constant horizontal component of speed 20 km/h over a washboard road with sinusoidal bumps. The amplitude and wavelength of the sine curve are 5.0 cm, and 20 cm, respectively. The distance between the front and back wheels is 2.4 m. Find the amplitude of oscillation of the automobile, assuming it moves vertically as an undamped driven harmonic oscillator. Neglect the mass of the wheels and springs and assume that the wheels are always in contact with the road.
Homework Equations
## \frac {d^2x} {dt^2} + 2\beta \omega_0 \frac {dx} {dt} + \omega_0^2x = F(t) ## (Driven Harmonic Oscillation) EQ1
## \frac {d^2x} {dt^2} + 2\beta \omega_0 \frac {dx} {dt} + \omega_0^2x = \frac 1 m F_0 sin(\omega t)## (Sinusoidal Driving Force) EQ2
## \beta = 0 ## (when undamped) EQ3
## F_{net} = ma = \sum F_x + \sum F_y ## (Newton's Second Law) EQ4
The Attempt at a Solution
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My main issue in this problem is first deriving the equation of motion, and expressing its general solution as well. The solution gives the answer for equation of motion as $$ m \frac {d^2 y} {dt^2} = -k(y-asin(\omega t))$$ and gives the general solution as $$ y(t) = Bcos(\omega_0 t +\beta) + \frac {a \omega_0^2} {\omega_0^2 - \omega^2} sin(\omega t)$$
My initial thought process is, okay, so this is a Driven Harmonic Oscillator with a Sinusoidal Driving Force, yet it is undamped. So I use equation 2, with the condition of equation 3. $$ \frac {d^2x} {dt^2} + \omega_0^2x = \frac 1 m F_0 sin(\omega t) $$
I have absolutely no idea what to do when I get here, besides it being a 2 dimensional differential equation that I don't know how to solve. So I tried using Newton's Second Law, and the forces are 0 within the x direction.
$$ F_{net} = m \frac {d^2x} {dt^2} = -mg - ky $$
I really feel as if this isn't right at all either. I just really need a direction to go in, and get that initial equation of motion.