You observed three different star clusters and found that the main-sequence turnoff stars in cluster 1 had spectral type a, the main-sequence turnoff stars in cluster 2 had spectral type b, and the main-sequence turnoff stars in cluster 3 had spectral type g. which star cluster is the oldest?

a.) cluster 1
b.) it is impossible to determine their ages given only the spectral types
c.) cluster 2
d.) cluster 3

Cluster 3 (D)

Explanation: Cluster 3 is the oldest and it could be the source from which cluster 2 and 3 got their spectral type from.

The answer is D, cluster 3

Explanation:

Firstly, we need to understand that star clusters are a group or category of stars bonding together through a form of gravitational force.  Streamlining down to a G-type star cluster, A G-type cluster is mostly refereed to as the yellow dwarf and this is because an example of a G-type star cluster is the yellow sun and because it is assumed that the sun is the oldest star, cluster 3 is the relative answer.

The car's speed was zero at the beginning of the 12 seconds,
and 18 m/s at the end of it.  Since the acceleration was 'uniform'
during that time, the car's average speed was (1/2)(0 + 18) = 9 m/s.

12 seconds at an average speed of 9 m/s  ==>  (12 x 9) = 108 meters .



That's the way I like to brain it out.  If you prefer to use the formula,
the first problem you run into is:  You need to remember the formula !

The formula is        D = 1/2 a T²

                   Distance = (1/2 acceleration) x (time in seconds)²

             Acceleration = (change in speed) / (time for the change)
                                  =        (18 m/s)            /        (12 sec)
                                  =                      1.5 m/s² .

                  Distance  =  (1/2 x 1.5 m/s²) x (12 sec)²
                                  =       (0.75 m/s²)  x  (144 sec²)  =  108 meters .