Question

Physics Help Please:
The drill used by most dentists today is powered by a small air-turbine that can operate at angular speeds of 350000 rpm. These drills, along with ultrasonic dental drills, are the fastest turbines in the world-far exceeding the angular speeds of jet engines. Suppose a drill starts at rest and comes up to operating speed in 1.9s .
A) What is angular acceleration. I already figured it out to be 3100rev/s^2
B) How many revolutions does the drill bit make as it comes up to speed?
Express your answer using two significant figures.

Answer 1

I only need help with B. I used the following equation: angular velocity=(change in theta/time); so I got (350000/60)rev/s=(Delta*Theta)/(1.9)

Answer 2

And I got the answer of 1.1*10^4 but it says I am wrong. Am I doing something wrong?

Answer 3

A) i get 3070 rev/s^2

B) at constant acceleration, you can use average speed 1/2 * ( 0 + 350 k) as the speed through the whole journey, and you already know the time, 1.9s. use proper units again and multiply those and you get total revs.

Answer 4

Thank You so much! You were right for B except that it should have been 1/2*(0+5833) instead of 1/2 * ( 0 + 350 k), because we had to convert 350000rpm to rps or rev/s which gives us 5833. It also said that my answer for question A was right. I got the answer for question A by converting rpm to rev/s, and then I used the angular version of the following formula: acceleration=(velocity/time). Again, thank you so much!