We are given:
Mass of the rocket = 10 kg
Weight of the Rocket = 100 N
Upward thrust applied by the rocket = 400 N
Net upward force on the rocket:
We are given that gravity pulls the rocket with a force of 100 N
Also, the rocket applied a force of 400N against gravity
Net upward force = Upward thrust - Force applied by gravity
Net upward force = 400 - 100
Net upward force = 300 N
Upward Acceleration of the Rocket:
From newton's second law:
F = ma
replacing the variables
300 = 10 * a
a = 30 m/s²