v = 45 - 9.81 t = 45 - 9.81(2.55) = 20 m/s
initial momentum up = 20 m
final momentum up = 20 m = (1/2)m v cos 45 + (1/2)m v cos 45
final up = initial up
m v cos 45 = 20 m
v = 20/cos45 = 20 sqrt 2
On new year eve,a fire work rocket is launched vertically into the night sky with an initial speed of45m/s .After 2.55s ,the coasting rocket then explode and break into two pieces with an equal mass .Each pieces follow trajectory of 45 degree to the verticle . Find their speed immediately after explosion.
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