Question

A 200 g model rocket is observed to rise 100 m above the ground after launch. What must have been the launch speed of the rocket at the ground?

Answer 1

the mass of the rocket does not matter.

Given a liftoff speed of v, the height

h(t) = vt - 4.9t^2
The max height is reached when t = v/9.8, so we have

v(v/9.8) - 4.9(v/9.8)^2 = 100
v = 44.27 m/s

Or, you could just use the formula for max height
h = v^2/2g and get

v^2/19.6 = 100
v = 44.27 m/s

Answer 2

THANKS