physics
posted by kwaku .
A 0.2 kg mass hangs at the end of a wire. what is the tension in the wire if the ball is whirled around in a horizontal circle with tangential velocity of 5 m/sec

Let the tension be T and the angle of the string to the horizontal be A.
Write equations for horizontal and vertical motion.
T sin A = M g
T cos A = M V^2/r
Square both sides and add the two equations to get T
T^2(sin^2A + cos^2A) = T
= M^2(g + V^2/r)
Solve for T.
You need to know the length of the wire (r) to solve this problem. They should have told you what it is. 
A person places the speakers 4.0 m apart and connects a signal generator to both speakers that produces a single and consistent tone. (constant wavelength and frequency) He then walks to a point that is 2.0 m from one speaker and 2.3 m from the other. At that point he notices a quiet “spot”. If the speed of the sound in the room is known to be 350 m/s, calculate the possible frequencies being played by the speakers.
My Answer:
PD=2.3m2m
PD=.3m
PD=(n.5) λ, but λ=v/f
PD=(n.5)(v/f)
.3=(n.5)(350/f)
f=(n.5)(350/.3)
f=(n.5)(3500/3)
f=(3500n/3)(3500/6)
f=(3500n/3)(3500/6), where n is any real integer.
Is this right? Thanks for your help.