Aboat heads north in still water at 4.5 m/s directly across a river that is running east at 3.0 m/s. what is the velocity of the boat with respect to earth?

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.

If an athlete runs once around a track, back to the starting line, her average velocity is zero. true or false?

What are the similarities & differences between a thermistor and a light dependent resistor in physics?