Acceleration=force/mass=28/(10+4)=2m/s^2
force10kg=ma=10*2
force4kg=ma=(10*2)=20
the4 kg is pushing against the 10kg block
vf=vi+at
-10=20*28/14 * t
t=30/2=15sec
i hope this can help you.
M=2.45 because you multiply out the equation on the right and divide by 10
Phonograph. Hope that helps
Omitting the 1 will not change the value of the number, but will change the units at the end of the problem