physics
posted by julia on .
i know how to do it, i keep getting the wrong answer!!
a bob of mass 4.00 kg is suspended from a fixed point by a massless string of length 1.50 m. The bob moves in a horizontal circle with the string always making an angle theta=22 from the vertical. what is the speed of the bob?
(tension is 42.3 N)

Look at the tension:
tension=mg/sinTheta
Now, the horizontal component of tension is tension*costheta, or mg/tantheta
That must equal centripetal force,
mv*2/radius.
the radius must be 1.50*sinTheta
so finally,
mv^2/1.5*sintheta =mg/tantheta
solve for v
check my thinking. 
thank you so much!! it was so frustrating to get the wrong answer after wrong answer..