Across country runner runs 20 km in 4 hours. what is his average speed

Which sentences describe disadvantages of burning fossil fuels instead of using hydrogen fuel cells? burning fossil fuels contributes to climate change. burning fossil fuels takes place inside expensive fuel cells. fossil fuels aren't widely available, but pure hydrogen is. fossil fuels are nonrenewable.

Apropagating wave in space with electric and magnetic components. these components oscillate at right angles to each other. it may travel in a vacuum. determine the term.

An electron in an x-ray machine is accelerated through a potential difference of 1.00 × 104 v before it hits the target. what is the kinetic energy of the electron in electron volts?