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Math Help - should i have used the mass in the working out

  1. #1
    prs
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    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

    2) theta=distance/radius= 9.42/1.5= 6.28 rads

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

    4)w2*radius= 2.09*1.5= 6.579 rad/s2 (ANGULAR ACCELERATION)

    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,,
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  2. #2
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by prs View Post
    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

    2) theta=distance/radius= 9.42/1.5= 6.28 rads

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

    4)w2*radius= 2.09*1.5= 6.579 rad/s2 (ANGULAR ACCELERATION)

    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 \alpha is zero rad/s^2. But I would check with your instructor on this.

    Knowing that \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 \omega of
    \displaystyle \omega = \frac{2 \pi r}{t}.

    -Dan
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  3. #3
    prs
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    Quote Originally Posted by topsquark View Post
    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 \alpha is zero rad/s^2. But I would check with your instructor on this.

    Knowing that \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 \omega of
    \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,,
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  4. #4
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by prs View Post
    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 \alpha, which is associated with the tangential accleration, with the centripetal acceleration.

    -Dan
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