air puck of mass m1 = 0.17 kg is tied to a string and allowed to revolve in a ci

Question

air puck of mass m1 = 0.17 kg is tied to a string and allowed to revolve in a circle of radius R = 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 m2 = 0.9 kg is tied to it (see the figure below). The suspended mass remains in equilibrium while the puck on the tabletop revolves.

(a) What is the tension in the string?
___ N

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

(c) What is the speed of the puck?
_____ m/s

Explanation / Answer

Mass of the air puck m1 = 0.15 kg

Radius of the circle r = 1.0 m

Suspended mass m2 = 1.2 kg

(a) Tension in the string

         T = m2 g = (1.2 kg) (9.8 m/s2)

                       = 11.76 N

(b) From Newton's laws the horizontal force acting on the puck is centripetal force which is equal to tension in the string

so   F = 11.76 N

(c) From centeripetal force

         F = m1v2/r

         11.76 N = (0.15 kg)v2/(1.0 m)

   Therefore the speed

            v =( 11.76 /0.15)

               = 8.85 m/s

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