Why is circular motion at constant speed not a natural state of motion?

The boy of mass 30 kg is at r1= 2 meters from the fulcrum. of the girl is 45 kg, at what r2 must she sit so that they are balanced ?

Steam enters an adiabatic diffuser at 150 kpa and 1208c with a velocity of 550 m/s. determine the minimum velocity that the steam can have at the outlet when the outlet pressure is 300 kpa.

Select all of the following that are equal to an impulse of 20 unitsa) force= 5, time= 5.5b) force= 25, time= 0.8c) force= 0.1, time= 200d) force= 10, time= 2(its b, c, and d)(also in order to find answer they have to add to get the unit)ex= 25x.8=20 or .1x200=20