You are riding in an automobile of mass 3000 \mathrm{~kg}. Assuming that you are examining the oscillation characteristics of its suspension system. The suspension sags 15 \mathrm{~cm} when the entire automobile is placed on it. Also, the amplitude of oscillation decreases by 50 \% during one complete oscillation. Estimate the values of (a) the spring constant \mathbf{k} and (b) the damping constant b for the spring and shock absorber system of one wheel, assuming that each wheel supports 750 \mathrm{~kg}.
You are riding in an automobile of mass 3000 \mathrm{~kg}. Assuming that you are examining the oscillation characteristics of its suspension system. The suspension sags 15 \mathrm{~cm} when the entire automobile is placed on it. Also, the amplitude of oscillation decreases by 50 \% during one complete oscillation. Estimate the values of (a) the spring constant \mathbf{k} and (b) the damping constant b for the spring and shock absorber system of one wheel, assuming that each wheel supports 750 \mathrm{~kg}.

(a) Mass of the automobile is given as =3000 \mathrm{~kg}

The suspension sags by a length of 15 \mathrm{~cm}

Decrease in amplitude =50 \% during one complete oscillation

If each spring’s spring constant is k, the spring constant of the four springs in parallel equals

\mathrm{K}=4 \mathrm{k}

Since F=4 k x

\mathrm{Mg}=4 \mathrm{kx}

\Rightarrow k=M g / 4 x=(3000 \times 10) /(4 \times 0.15)=5 \times 10^{4} \mathrm{~N}

(b) Each wheel supports 750 \mathrm{~kg} weight

\mathrm{t}=2 \pi \sqrt{\mathrm{m}} / \sqrt{\mathrm{k}}=2 \times 3.14 \times\left(\sqrt{\left.750 / \sqrt{5} \times 10^{4}\right)}=0.77 \mathrm{sec}\right.

Using, x=x_{0} e^{-\frac{b t}{2 m}},

we get

\frac{50}{100} x_{0}=x_{0} e^{-\frac{6 \times 0}{2 \times 75}}

\log _{e} 2=(b \times 0.77) /(1500) \log _{e} e

b=\frac{(1500) \log _{c} 2}{0.77}

\mathrm{b}=(1500 \times 0.6931) / 0.77=1350.2 \mathrm{~kg} / \mathrm{s}