- #1
SpaceExplorer
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A puck of mass 'm' on friction-less ice is attached by a horizontal string of
length 'l' to a very thin vertical pole of radius R. The puck is given a kick
and circles around the pole with initial speed V. The string wraps around the
pole, and the puck gets drawn in and eventually hits the pole. What quantity
is conserved during the motion? What is the puck’s speed right before it hits
the pole?
The answer has to be 'V', right? Because the only thing being conserved here is the 'kinetic energy', since no external force is applied nor there's any extra work done by 'friction'. There's a torque acting on 'm' at each point, so 'angular momentum' can't be conserved.
length 'l' to a very thin vertical pole of radius R. The puck is given a kick
and circles around the pole with initial speed V. The string wraps around the
pole, and the puck gets drawn in and eventually hits the pole. What quantity
is conserved during the motion? What is the puck’s speed right before it hits
the pole?
The answer has to be 'V', right? Because the only thing being conserved here is the 'kinetic energy', since no external force is applied nor there's any extra work done by 'friction'. There's a torque acting on 'm' at each point, so 'angular momentum' can't be conserved.