A(n) is a collection of 105 to 106 stars in a region 10 to 30 pc in diameter. the stars in the collection tend to be more than 109 years old and mostly yellow and red stars.

Open cluster

Explanation:

Open cluster is the group of stars of number up to few thousand which were formed from same cloud and had approximately same age. They are mostly red and yellow stars and these stars are bound loosely by the mutual gravitational attraction and the stars become disrupted by the close encounters with other clouds of gas and clusters ss these stars orbit galactic center.

can be answered using momentum.

momentum = p

p1= mass1 * velocity1

p1 = p2

therefore

p1 = 6kg * 4m/s

p1 = 24kgm/s

p2=m2 * v2

24 kgm/s = 7kg * v2

v2 = 24 kgm/s / 7kg

v2= 3.42 m/s

not too sure thinking all accelerations are pointed down