1. A rotor used in an AC motor manufactured by the Toole N. Di Company has a time to failure that is lognormal with an MTTF found to be 3600 operating hours and a shape parameter s equal to 2.

Current preventive maintenance practices require the rotor to be replaced every 100 operating hours. Determine the probability that a rotor will survive the 100 hr.

If at the end of the 100 operating hours the maintenance departments neglects to replace the rotor, what is the probability that it will survive until the next scheduled replacement (assume that it has not failed at 100 hr)?

If the rotor is still operating after 200 hr, should it be replaced?

From the above analysis, what can you say about the hazard rate and the preventive maintenance policy?