A wheel which is initially at rest is subjected to a constant angular acceleration about its axis. It rotates through an angle of `15^@` in time t sec. The increase in angle through which it rotates in the next 2t sec is

Options

A. `90^@`
B. `120^@`
C. `30^@`
D. `45^@`

Answer

B

Explanation

If angular acceleration is constant,`theta =omega_(0)t+ ½ alpha t^(2)`
`theta propto t^(2)`
`theta = 15^@ implies 15 propto t^(2)`
For total time of 3t
` theta propto (3t)^(2) implies 15xx9+135^@`
For 2t time,
`therefore` Angle, `theta = 135^@ - 15^@ = 120^@`