Answer:They are used to transmit short or long or FM wavelength radio waves. They are used to transmit TV or telephone or wireless signals and energies. They are responsible for the transmission of energy in the forms of microwaves, visible light, infrared radiation, ultraviolet light, gamma rays and also X-rays.
Explanation:
Answer:
D
Explanation:
Increasing its height to twice its original value
Answer:
The net force is zero
Explanation:
When an object is falling, there are two forces acting on it:
- The force of gravity, which is equal to the weight of the object, which pushes the object downwards
- The air resistance, which acts against the motion of the object, so it pulls upward
While the magnitude of the force of gravity is constant, the magnitude of the air resistance increases as the velocity of the falling object increases: at some point of the motion, the air resistance becomes equal in magnitude to the force of gravity. At this point, the net force on the object becomes zero, and according to Newton's second law, the acceleration of the object becomes also zero:

But zero acceleration means that the velocity of the object is now constant: this is known as terminal velocity.
Explanation:
When a bullet is fired from a rifle, the actual firing makes a distinctive sound, but people at a distance may hear a second because the bullet creates a shock wave , a little sonic boom( speed of this sonic boom is greater than the speed of sound). It is this sound only that is heard by the people at a distance from the gun.