A man runs the Boston marathon (43.7km) in 4 hours. Calculate his average velocity in m/s.

How does a hydroelectric power plant converts energy into energy.

Which process does not require the presence of a physical substance in order to transfer heat? air in the atmosphere is heated by the ground. this warm air then rises, and cooler air falls. this is an example of what type of process? how is conduction different from radiation?

In a ball-and-stick molecular model, what do the sticks represent?