Amachinist turns the power on to a grinding wheel, which is at rest at time t = 0.00 s. the wheel accelerates uniformly for 10 s and reaches the operating angular velocity of 80 rad/s. the wheel is run at that angular velocity for 39 s and then power is shut off. the wheel decelerates uniformly at 2.6 rad/s2 until the wheel stops. in this situation, the time interval of angular deceleration (slowing down) is closest to:

Consider an ordinary, helium-filled party balloon with a volume of 2.2 ft3. the lifting force on the balloon due to the outside air is the net resultant of the pressure distribution exerted on the exterior surface of the balloon. using this fact, we can derive archimedes’ principle, namely that the upward force on the balloon is equal to the weight of the air displaced by the balloon. assuming that the balloon is at sea level, where the air density is 0.002377 slug/ft3, calculate the maximum weight that can be lifted by the balloon. note: the molecular weight of air is 28.8 and that of helium is 4.