Answer:
2.75 N
Explanation:
Given that,
Box A has a mass 21.0 kg and box B has a mass 8.0 kg.
A horizontal force of 100N is exerted on box A.
Let a be the acceleration of the system. Using second law of motion,

Now applying Newton's second law to box B. So,

So, 2.75 N is the force that box A exerts on box B.
Answer:
Ball will not hit bell.
Explanation:
The height of the ball is modeled by the equation h(t)= -16t²+39t
We need to find if the bell is 25 ft above the ground, will it be hit by the ball.
So we need to find maximum height of the ball.
For maximum height we have

Substituting in h(t) = -16t²+39t
Maximum height reached = h(1.22) = -16 x 1.22²+39 x 1.22 = 23.77 ft
So maximum height reached is less than height of bell.
Ball will not hit bell.
Answer:

Explanation:
Given that,
The half-life of Barium-139 is 
A sample contains
nuclei.
We need to find the decay constant for this decay. The formula for half life is given by :

Put all the values,

So, the decay constant is
.
Answer:
q = 8472.2 W/m
Explanation:
The solving or solution is given in the attach documents.
<h2>
Answer: It is the result of a mixture of radiation from many independent sources, such as stars and galaxies. </h2>
Microwave background radiation was accidentally discovered by Penzias and Wilson on 1964. This is a form of electromagnetic radiation that <u>is present in the </u><u>whole universe</u><u> and completely fills it (it is isotropic)</u>.
<h2>
It is the leftover radiation from the big bang.
</h2>
Its frequency belongs to the microwaves range and is one of the main demonstrations of the of the Big Bang theory model.
It is important to note the Big Bang occurred 400,000 years before the events related to the microwave cosmic radiation, this means the Big Bang occurred first.