An automobile engine slows down from 4500 rpm to 1600 rpm in 6.0 s. (a) calculate its angular acceleration, assumed constant. 3036.87 incorrect: your answer is incorrect. rad/s2 (b) calculate the total number of revolutions the engine makes in this time. 8700 incorrect: your answer is incorrect. rev

1) The angular acceleration of the engine is given by:

where  and  are the final and initial angular velocity of the engine, while  is the time interval considered.
We need first to convert the velocities from rpm (revolutions per minute) into rad/s. Keeping in mind that 


The factor of conversion is

So, the two velocities become


And using  we can find the angular acceleration of  the engine:

where the negative sign means the engine is decelerating.

2) The total number of revolutions is given by the law of angular motion:


And keeping in mind that , the number of revolutions is

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