Answer:
78.4 J
Explanation:
The gravitational potential energy of the ball (relative to the ground) is given by
where
m = 2 kg is the mass of the ball
g = 9.8 m/s^2 is the acceleration due to gravity
h = 4 m is the height of the ball above the ground
Substituting numbers into the formula, we find
They travel the slowest through gasses
Wave-speed = (wavelength) x (frequency)
Speed = (20.0 meters) x (3.00 / second)
Speed = 60 meters/second
Cellular telephone service, television, garage-door openers, toy walkie-talkies, RC model airplanes and boats, taxi communication, ambulance communication, police communication, fire communication, cordless telephones, wireless headphones, 'microwave' ovens, and Bluetooth stuff, all radio waves to transmit and receive their signals.
None of these use 'microwaves' ... not even 'microwave' ovens. 'Microwave' is a label for radio at frequencies above 3 GHz, and none of these things operate at frequencies that high. Bluetooth and microwave ovens operate around 2.45 GHz.
Wi-Fi has one set of channels around 2.4 GHz ... radio waves but not microwaves. Wi-Fi also has another set of channels around 5 GHz ... radio waves that can properly also be called 'microwaves'.
Some TV remotes use infrared waves to communicate with the TV set.
We don't (yet ?) manufacture anything that uses ultraviolet rays, X-rays, or gamma rays for communication. Even if we knew how, these forms of radiation are too dangerous to go shining them around all over the place where people are.
