Which of these holds a galaxy together? a. disk b. gravity c. open clusters d. globular clusters

'Disk', 'open cluster', and 'globular cluster' are shapes into which stars gather themselves.  

For holding big groups of stars together, we have to find some kind of force. 'Gravity' does the job nicely.  (B)

this could be newton#'s law of cooling. the cooling curve is exponential

we're given that v₀ = 0 and a = 5.4 m/s². therefore, since v = at + v₀ for constant acceleration the equation for velocity is

after 28s,

m/s

which i would round to 150 m/s as my final answer