Rotational Motion Tension at the bottom of the circle

[physgrl]

Homework Statement

9. A 0.61 kg mass attached to the end of a 0.50 m cord rotates in a vertical circle. The angular speed of the mass at the bottom of the circle is 2π rad/s. The tension in the string at this point is:

a. 18 N

b. 21 N

c. 12 N

*d. 54 N

Homework Equations

W=mg
F=ma
a_centripetal=v²/r
v=ωr

The Attempt at a Solution

I used F_tension=F_centripetal+W and I got 18N the answer key says its 54N

 

[Andrew Mason]

I agree with your answer.

AM

 

[LawrenceC]

Same here. I think the supplied answer is incorrect.

 

[physgrl]

Thanks :)