What is the centripetal force necessary to keep a 0.4 kg object rotating in a circular path of radius 3m?

The density of a liquid could be found by using

Aboat radioed a distress call to a coast guard station. at the time of the call, a vector a from the station to the boat had a magnitude of 45.0 km and was directed 15.0° east of north. a vector from the station to the point where the boat was later found is = 30.0 km, 15.0° north of east. what are the components of the vector from the point where the distress call was made to point where the boat was found? in other words, what are the components of vector c = b - a?

What is the coefficient of kinetic friction μk between the block and the tabletop?