Rotational Motion: Calculating Time to Reach 750 RPM

[hannah12345]

Homework Statement

A 1.5 hp motor drives a machine disk having a mass of 4.5 kg and a diameter of .4 m from rest to a speed of 750 rpm. How long does it take to reach the operating speed?

Homework Equations

angular momentum
torque

The Attempt at a Solution

I'm not really sure where to start with this problem. I don't know how to find time without distance or acceleration. I tried solving for acceleration but I'm not sure how horsepower relates to torque.

 

[haruspex]

How much energy will the disk have at operating speed?

 

[hannah12345]

How would I use that to find time?

 

[haruspex]

How would I use that to find time?

What is the relationship between power, energy and time?