It is a screw. Hope this helps!
Since the biker is moving at constant speed
so we will have

here we know that

time = 4 second
now we have

now at the top point it feels free fall
so it is




so height of the bike at the top is same as diameter


Yes it will hurt on falling from this height
The speed of an object in a mass-spring system is given under the function

Here,
m = mass
k = Spring constant
A = Amplitude
x = Position
When the position is at the equilibrium point (x = 0), the speed will be maximum, and could even be expressed as

So the correct answer is B.