How does convection, conduction and radiation occur in a solar water heater?

At what point the certain object feels zero garvitational force between earth and the moon. take the required information from the book. required: distance away from earth or moon

The density of a substance is 4.0 g/cm3. if a sample of the substance has a volume of 25 cm3 then what is the mass

Ahot-air balloonist, rising vertically with a constant speed of 5.00 m/s releases a sandbag at the instant the balloon is 40.0 m above the ground. after it is released, the sandbag encounters no appreciable air drag. compute the velocity of the sandbag at 0.250 s after its release.