Air Puck Correct Method or not

1. Jul 16, 2007

rash219

Air Puck !!! Correct Method or not...

1. The problem statement, all variables and given/known data

An air puck of mass 0.25kg is tied to a string and allowed to revolve in a circle of radius 1.0m 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 1kg 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 string ?
c. What is the speed of the puck ?

2. Relevant equations

$$\Sigma$$F = m * a
F_c = (m * v^2) / r
a_c = v^2 / r

3. The attempt at a solution

a.
$$\Sigma$$F_y = m * a = 0
T - mg = 0
T = mg = 1.0kg * 9.8m/s^2 = 9.8N

b.
F_c = Tension on th string = 9.8N

c.
F_c = (m * v^2) / r = 9.8N
(0.25kg * v^2) / 1.0m = 9.8N
v = $$\sqrt{39.2}$$ = 6.3 m/s

Is this correct......THANKS!!!

Last edited: Jul 16, 2007
2. Jul 17, 2007

andrevdh

You seem to have it under control.

3. Jul 17, 2007

GoldPheonix

3a. is correct, but it has incorrect --as near as I can tell- reasoning. Just recall Newton's Third Law for centripetal forces. Also, for 3b. it asks what is the horizontal force is; which requires an angle for the center of the system; not certain on how you are supposed to acquire that answer.

Last edited: Jul 17, 2007
4. Jul 17, 2007

rash219

Thanks a lot !!!

5. Sep 24, 2007