The spring constant is computed by:
F = kx
Where: F is the force applied in newtons (N)
k is the spring constant measured in newtons per meter (N/m); and
x is the distance the spring is stretched (m)
and
F = mg
Where: F is the force pulling objects in the direction of the Earth.
m is the mass of the object.
g is the acceleration due to gravity;
So plugging our values in the formula:
F = mg
= (1.8) (9.81) = 17.658N
k =
F/x = 17.658 /0.09 = 196.2 N/meter
You would end up with a brown/black color depending on how much of each pigment was added! Hope this helps.
Answer:B
Explanation:
Given
speed of car 
mass of clump 
Radius of car tire 
Since the tire is rotating about axle so a centripetal force is acting constantly on each particle towards the center of tire.
Centripetal force is given by
where 
(inward)
Explanation:
They probably put "rolls without slipping" in there to indicate that there is no loss in friction; or that the friction is constant throughout the movement of the disk. So it's more of a contingency part of the explanation of the problem.
(Remember how earlier on in Physics lessons, we see "ignore friction" written into problems; it just removes the "What about [ ]?" question for anyone who might ask.)
In this case, you can't ignore friction because the disk wouldn't roll without it.
As far as friction producing a torque... I would say that friction is a result of the torque in this case. And because the point of contact is, presumably, the ground, the friction is tangential to the disk. Meaning the friction is linear and has no angular component.
(You could probably argue that by Newton's 3rd Law there should be some opposing torque, but I think that's outside of the scope of this problem.)
Hopefully this helps clear up the misunderstanding for you.
