Arun
Last Activity: 7 Years ago
To sustain circular motion the tension in the string should be non zero at every point, else the string will become slack and the mass will fall straight down instead of circular motion.
Now, tension is lowest at the top, hence if the tension is greater than zero at the top then surely it will be greater than zero at every other point. That is, if the string is to become slack, it will do so at the top (where its most vulnerable to become slack). Hence using this (tension at the top as zero) condition we find velocities at every other point.