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.
Answer: C
Explanation: Density= mass/volume
if dividing by same volume, need to increase mass in order to increase density.
same as 4=8/2 vs 8=16/2
increase numerator= increase in answer
Answer: kinetic energy is energy in motion
Explanation:
I got it right on my energy test
solution
In This question we have given ,
Charge on each ball=
force of repulsion between balls is 
Let distance between ball be x
We know by Coulombs law,
..............(1)
here,
Put values of k and charges in equation 1
therefore distance between two given charges is =.701m
