Please help ... General Physics?

Question

An air puck of mass 0.25 kg is tied to a string and allowed to revolve in a circle of radius 1.0 m on a frictionless horizontal table. The other end of the string passes through a hole in the center of the table, and a mass of 1.0 kg is tied to it. The suspended mass remains in equilibrium while the puck on the tabletop revolves.

(a) What is the tension in the string?

(b) What is the horizontal force acting on the puck?

(c) What is the speed of the puck?

I have uploaded a figure in the following link

http://rapidshare.com/files/73189156/figure.jpg.html\

Answer 1

Start by looking at FBDs of each component. The tension in the string is T
and without any friction, it is constant anywhere
since the 1.0 kg mass is in equilibrium, the tension in the string is
1*9.8 =9.8 N

Now look at the puck in a rotational frame of reference
I assume it is traveling at a constant speed
There are two horizontal forces balanced on the puck
the tension in the string, 9.8 N
and the centripetal force
m*v^2/r
since the forces balance
m*v^2/r=9.8
solving for v
v=sqrt(9.8*1/0.25)
v=6.26 m/s

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