We have that the spring constant is mathematically given as

Generally, the equation for angular velocity is mathematically given by

Where
k=spring constant
And

Therefore

Hence giving spring constant k

Generally
Mass of earth 
Period for on complete resolution of Earth around the Sun


Therefore


In conclusion
The effective spring constant of this simple harmonic motion is

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Since the car is at rest, the force experienced by car will be normal face(exerted by surface to which car is in contact) and weight of the car.
As the car is at rest, net force on the car should be zero.
Answer:
Explanation:
F = mω²R
F = 15(2π/8.5)²(7.8)
F = 63.93044788...
F = 63.9 N
answer a) is the closest. No idea how they got a value that low unless they used a poor approximation for π.
Pretty sure it’s halogens , or groups 14-17