3. A car does an emergency stop from 144 km\h in 4s What was its deceleration?
1 answer:
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(a) The angular acceleration of the wheel is given by
where
and 
are the initial and final angular speed of the wheel, and t the time.
In our problem, the initial angular speed is zero (the wheel starts from rest), so the angular acceleration is
(b) The wheel is moving by uniformly rotational accelerated motion, so the angle it covered after a time t is given by
where
is the initial angular speed. So, the angle covered after a time t=3.07 s is
where
In our problem, the initial angular speed is zero (the wheel starts from rest), so the angular acceleration is
(b) The wheel is moving by uniformly rotational accelerated motion, so the angle it covered after a time t is given by
where