A car is moving at a speed of `72 km//h`. The diameter of its wheels is `0.5 m`. If the wheels are stopped in `20` rotations by applying brakes, calcualte the angular retardation produced by the brakes.

Options

A. `-25.5"rad/s"^(2)`
B. `-29.5"rad/s"^(2)`
C. `-33.5"rad/s"^(2)`
D. `-45.5"rad/s"^(2)`

Answer

A

Explanation

`v=72xx(5)/(18)=20` m/s : `omega_(0)=(v)/(r)=(20)/(0.25)=80` rad/sec
`theta=2pixx20=40pi` rad
`omega^(2)=omega_(0)^(2)+2alphatheta`
`implies alpha=-((80)^(2))/(2xx40pi)=(-80)/(pi)=-25.5` rad/sec .