Answer:
Second Trial satisfy principle of conservation of momentum
Explanation:
Given mass of ball A and ball B 
Let mass of ball
and
Final velocity of ball 
Final velocity of ball 
initial velocity of ball 
Initial velocity of ball 
Momentum after collision 
Momentum before collision 
Conservation of momentum in a closed system states that, moment before collision should be equal to moment after collision.
Now, 
Plugging each trial in this equation we get,
First Trial

momentum before collision
moment after collision
Second Trial

moment before collision
moment after collision
Third Trial

momentum before collision
moment after collision
Fourth Trial

momentum before collision
moment after collision
We can see only Trial- 2 shows the conservation of momentum in a closed system.
Answer:
Explanation:
Matter can be broken down into two categories: pure substances and mixtures. Pure substances are further broken down into elements and compounds. Mixtures are physically combined structures that can be separated into their original components. A chemical substance is composed of one type of atom or molecule.
Answer: 168.75 N
Explanation:
first, let's convert microcoulombs to coulombs
q1 = 1e-4 C
q2 = 3e-5 C
r = 0.4 m
then use the equation Fe = 
plug in values --> F = (9e9*1e-4*3e-5)/(0.4)^2
F = 168.75 N