Imagine a car crash. A car coming at a high speed has a head on collision with a car at rest. When the car makes impact, it will move the other car with it at a slower speed then it was travelling at. In this case, the velocity decreased since the car slowed down, but the mass increased since there are now two cars moving. Momentum was conserved because the change in mass accounts for the loss of velocity.
# 7 the answer is 4) because you need opposites in order to attract
# 8 I'm going to guess it is 4) because electricity is needed in order a light bolt to work.(don't take my word for this one I'm not sure but, the other answer are correct)
# 9 the answer is 4) because the comb dose collect negative charges from the hair in order to make the hair have positive charge.
Hope this helped : )
Answer: 2.67 m/s
Explanation:
Given
Mass of block A is 
mass of block B is 
The initial velocity of block A 
the initial velocity of block B is 
After collision velocity of block A is 
Conserving momentum

The momentum of block A after the collision is 
Therefore, there is no change in sign.
Answer: question 1 , would be one question 2 , would be 1 joule and number three would be number one and number four would be , power and last one would be, number two
Explanation: sorry if its wrong