A radio wave is generated by a transmitter and then detected by a receiver. An antenna allows a radio transmitter to send energy into space and a receiver to pick up energy from space. Transmitters and receivers are typically designed to operate over a limited range of frequencies
Answer;
C.It is the minimum amount of material needed to sustain a fission reaction.
Explanation;
-A critical mass is the smallest or the minimum amount of fissile material needed for a sustained nuclear chain reaction. A critical mass must be achieved in order for the chain reaction to continue and release the atomic energy. A critical mass is needed for both a nuclear reactor and an atomic or hydrogen bomb.
-The critical mass of a fissionable material depends upon its nuclear properties (specifically, the nuclear fission cross section), its density, its shape, its enrichment, its purity, its temperature, and its surroundings.
Answer:
= 351.84 J
Explanation:
Using the conservation of energy K:

so:

where m is the mass, v the initial velocity,
is the kinetic energy of the mass as it clears the fence, g the gravity and h the altitude.
Then, replacing values, we get:

solving for
:
= 351.84 J