Angular Acceleration Help?

Question

A rotating object has an angular acceleration of α = 0 rad/s2. Which one or more of the following three statements is consistent with a zero angular acceleration?
A. The angular velocity is ω = 0 rad/s at all times.
B. The angular velocity is ω = 10 rad/s at all times.
C. The angular displacement θ has the same value at all times

I thought it was A and B, but apparently that is wrong.

2. The drawing shows a top view of a square box lying on a frictionless floor. Three forces, which are drawn to scale, act on the box. Consider an angular acceleration with respect to an axis through the center of the box (perpendicular to the screen). Which one of the following statements is correct?
This is the link to the picture...
http://s3.amazonaws.com/answer-board-image/7da67e71-fadd-4eca-a469-239090afd5ef.gif

A. The box will have a translational acceleration, but not an angular acceleration.
B. It is not possible to determine whether the box will have a translational or an angular acceleration.
C. The box will have neither a translational nor an angular acceleration.
D. The box will have both a translational and an angular acceleration.
E. The box will have an angular acceleration, but not a translational acceleration.

Answer 1

B. The angular velocity is ω = 10 rad/s at all times.



with 0 acceleration, angular velocity is constant



C. The box will have neither a translational nor an angular acceleration.

(drawn to scale)both "vertical" and "horizzontal" vectors become "0" .. no accelaration either angular or "translationiional"



(just my guess)



edit: the person who said "E" is probably correct ... it's "off center", one of the forces ... so even tho the vectors add up to zero [no motion of the "center of mass"] ,,, but if the "mass" was centered along that "off-center" force-vector, it "might" have a different result .... but the ther guy is still probly correct

Answer 2

first one is B, for the object is rotating, therefore meaning there is a velocity, and since acceleration is zero, it is constant velocity.



For 2, i believe it is E, for the net force is equal to zero, therfore now translational acceleration. However, F1 is not from the center of mass, therefore contributing to some torque, thus angular acceleration

Answer 3

the second one is E



The horizontal component of F3 is balanced by F1, and the vertical component of F3 is balanced by F2. Thus, the net force and, hence, the translational acceleration of the box, is zero. For an axis of rotation at the center of the box and perpendicular to the screen, the forces F2 and F3 produce no torque, because their lines of action pass through the axis. The force F1 does produce a torque about the axis, so the net torque is not zero and the box will have an angular acceleration.

Answer 4

B





C