Answer:
D. crystalline solid that conducts current under certain conditions
Explanation:
Semiconductors are crystalline solids that has the ability to conduct electrical currents but on certain conditions e.g heat. The conduction of semiconductors is less than that of conductors (metals) but more than insulators (nonmetals), hence, they are said to be intermediates of conductors and insulators in terms of electrical conductivity.
Examples of semiconductors are silicon, boron, carbon, germanium, arsenic etc.
An airplane is flying at a constant speed in a positive direction. It slows down when it approaches the airport where it's going to land. this is an example of negative acceleration (D).
The force is -12,000 N
Explanation:
First of all, we calculate the acceleration of the ball, by using the following suvat equation:

where:
v = 0 is the final velocity of the baseball (it comes to rest)
u = 40 m/s is the initial velocity
a is the acceleration
s = 2.0 cm = 0.02 m is the displacement of the ball
Solving for a,

Now we can calculate the average force exerted on the ball, by using Newton's second law:

where
m = 300 g = 0.3 kg is the mass of the ball
is the acceleration
Substituting,

where the negative sign indicates that the direction of the force is opposite to the direction of motion of the ball.
Learn more about forces:
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Answer:
the height of the potential energy is 3,200 J
Explanation:
The computation of the kinetic energy is shown below:
Kinetic energy = 1 ÷ 2 × mass × velocity^2
= 1 ÷ 2 × 4 kg × 40 m/s^2
= 3,200 J
Hence the height of the potential energy is 3,200 J
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