Flames Puck
uniform circular motion?
The figure below shows a 94 g puck revolving in a 20.8 cm radius circle on a frictionless table. The string passes through a hole in the center of the table and is tied to two 195 g weights.
(a) Suppose a flame burns through the string and causes the lower weight to fall off while the puck is revolving.
What will be the puck's speed after the weight drops?
(b) What will be the radius of its trajectory after the weight drops?
(a) F = Mg, where M is the weight of the weights = 2 x 195 g
F = ma, where m is the mass of the puck = 94 g
a = v²/R, where v is the velocity of the puck, and R is the radius of the circle which the puck is revolving.
mv²/R = Mg
v = sqrt[(M/m)Rg] = 2.91 m/s
(b) Use conservation of angular momentumn
L(i) = L(f)
I(i)(v/R) = I(f)(v/r)
(M+m)R = mr
r = ((M+m)/m)R
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