# Thread: should i have used the mass in the working out

1. ## should i have used the mass in the working out

calculate the angular acceleration and the angular velocity of a 2kg mass object rotating in a circle of 1.5m in a time of 3 seconds,

1) pi x 3 = 9.42m

3)w= theta/time= 6.28/3= 2.09 rads/s (ANGULAR VELOCITY)

could somebody tell me if i,ve got any of this right,and should i have included the mass of the object somewere in the working out,
,, thanks for any input,,

2. Originally Posted by prs
calculate the angular acceleration and the angular velocity of a 2kg mass object rotating in a circle of 1.5m in a time of 3 seconds,

1) pi x 3 = 9.42m

3)w= theta/time= 6.28/3= 2.09 rads/s (ANGULAR VELOCITY)

could somebody tell me if i,ve got any of this right,and should i have included the mass of the object somewere in the working out,
,, thanks for any input,,
I'm not sure what you are doing with 1) and 2), but we have no information to decide if there is an angular acceleration at all. Without anything being said about it I would assume that the $\displaystyle \alpha$ is zero rad/s^2. But I would check with your instructor on this.

Knowing that $\displaystyle \alpha$ is zero we have that the object moves in a circle of r = 1.5 m in t = 3 s. Thus you have a constant $\displaystyle \omega$ of
$\displaystyle \displaystyle \omega = \frac{2 \pi r}{t}$.

-Dan

3. Originally Posted by topsquark
I'm not sure what you are doing with 1) and 2), but we have no information to decide if there is an angular acceleration at all. Without anything being said about it I would assume that the $\displaystyle \alpha$ is zero rad/s^2. But I would check with your instructor on this.

Knowing that $\displaystyle \alpha$ is zero we have that the object moves in a circle of r = 1.5 m in t = 3 s. Thus you have a constant $\displaystyle \omega$ of
$\displaystyle \displaystyle \omega = \frac{2 \pi r}{t}$.

-Dan

Thanks for that dan,

as for 1 and 2 steps , i divided pi (3.14) by the diameter to get the circle length, then the circle length by the radius to get the angle subtended by the arc, then this was divided by the time to get radians per second for angular velocity,

as for the angular acceleration i first thought that there is no change in it,its ( constent) but velocity is a vector force and vector direction is changing,

so with formalua you posted have i got this right,, 2pi*1.5/3=3.142 rad/s for angular velocity,

thanks again,,

4. Originally Posted by prs
as for the angular acceleration i first thought that there is no change in it,its ( constent) but velocity is a vector force and vector direction is changing,
You are confusing the angular acceleration $\displaystyle \alpha$, which is associated with the tangential accleration, with the centripetal acceleration.

-Dan