Kilowatt-hour(kWh) is a unit of

Options

A. Current
B. Power
C. Energy
D. Resistance

Answer

C

Explanation

Here conservation of angular momentum takes place about centre O
`therefore` Angular momentum L = constant
`therefore ` Initial kinetic energy = `(L^(2))/(2I)`
`=(L^(2))/(2mr^(2))("where "I=mr^(2))...(1)`
Final kinetic energy after pulling the string
`=(L^(2))/(2m(r.)^(2))`
but `r.=(r )/(2)`
`therefore` Final kinetic energy = `(L^(2))/(2m((r^(2))/(4)))`
`=(4L^(2))/(2mr^(2))`
`=4((L^(2))/(2mr^(2)))`
`=4xx` initial kinetic energy
Hence, kinetic energy of mass will increase by a factor of 4.