A block of mass m tied with a string moves in a vertical plane. A constant vertical upward force F = 3mg (Besides weight mg donward) always acts on the block during its vertical circular motion. What should be the minimum speed (in m/s) at highest point of circle so that the block completes the circular motion. Given length of rod = 25 cm.

Answer

2

Explanation

KE at `B=(1)/(2)mv^(2)`
= loss in PE = mg R `(cosalpha-sin beta)`
at B , N = 0, mg `sinbeta=(mv^(2))/(r)`
`=2 mg (cosalpha-sinbeta)`
`3 sin beta=2cosalpha`