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mrknowknow
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Homework Statement
I need help deriving some formulas, specifically the theoretical speed of a bob at the bottom of a pendulum where the string is horizontal from the lower rod to the bob.
Background / Introduction
1. A small weight at the end of a string of length, L, forming a simple pendulum.
2. A horizontal rod is located a distance, d, directly beneath the pivot point.
3. The mass is held so that the string is taut and horizontal and then let fall.
4. What is the minimum distance, d, such that the mass will cause the string to loop over the pin at least once? In theory, we assume the bob is a point mass and the horizontal rod which is a distance d from the fulcrum is infinitesimally thin. However, experimentally, we are looking for the minimum value of d such that the mass hits the lower rod and falls on the other side of it.
Some Physics principles to keep in mind:
• Since the only considered forces acting on the mass are tension and weight, and since the tension does no work on the mass (the tension is perpendicular to the displacement), energy of the mass is conserved.
• Once the string goes slack, the tension disappears and the only force acting on the bob is the force of gravity. Thus, the mass is in projectile motion.
• At the point of the string going slack, the tension drops to zero, but at that moment there is still a centripetal force.
Position Meaning
A Starting position. String is horizontal from the upper rod to the mass.
B At bottom of arc. String is vertical from the upper rod to the mass.
C String is horizontal from the lower rod to the mass
D String starts having slack
E Mass just barely makes it over the lower rod.
Homework Equations
the only equation I've been able to derive is at is V=sqrt(g(L-D)