What is the spring constant of each spring

[rayhan619]

Homework Statement

A compact car has a mass of 1200 kg. Assume that the car has one spring on each wheel, that the spring are identical, and that the mass is equally distributed over the four springs. draw a picture of the situation.
a) what is the spring constant of each spring if the empty car bounces up and down 2.0 times per second?
b) what will be the cars oscillation frequency while carrying four 70 kg passengers.

Homework Equations

f = 1/2pie(k/m)^sq root

The Attempt at a Solution

m = 1200 kg
f = 2 hz

a) k = (2*pie*f)^2 * m = (2*3.14*2hz)^2*1200 kg = 189304.32 N/m

b) m = (4*70)+1200 kg = 1480 kg

f = (1/2*pie)(189304.32 Nm^-1/1480 kg) = 1.8 hz

im not sure where I messed up.

 

[Doc Al]

a) k = (2*pie*f)^2 * m = (2*3.14*2hz)^2*1200 kg = 189304.32 N/m

There are four springs, not one giant spring.

 

[rayhan619]

so divide k by 4?

 

[Doc Al]

Yes.

 

[rayhan619]

so
a) k = (189304.32 N/m)/4 = 47326.08 N/m

and
b) f = (1/2*pie)(47326.08 Nm^-1/1480 kg)^sq. root = 0.9 hz

is it right?

 

[Doc Al]

so
a) k = (189304.32 N/m)/4 = 47326.08 N/m

OK.

and
b) f = (1/2*pie)(47326.08 Nm^-1/1480 kg)^sq. root = 0.9 hz

No. What's the mass per spring?