A model rocket is fired vertically from rest. It has a net acceleration of 16.0

Question

A model rocket is fired vertically from rest. It has a net acceleration of 16.0 m/s2. After 1.9 s, its fuel is exhausted and its only acceleration is that due to gravity.

The model rocket has a mass of 94 g and you may assume the mass of the fuel is much less than 94 g.
(a) What was the net force on the rocket during the first 1.9 s after liftoff?
magnitude __?__N
direction (upward/downward?)

(b) What force was exerted on the rocket by the burning fuel?
magnitude __?__N
direction (upward/downward?)

(c) What was the net force on the rocket after its fuel was spent?
magnitude __?__N
direction (upward/downward?)

(d) The rocket's vertical velocity was zero instantaneously when it was at the top of its trajectory. What were the net force and acceleration on the rocket at this instant?
-Net force:
--magnitude __?__ N
--direction (upward/downward?)
-Acceleration:
--magnitude __?__ m/s2
-direction (upward/downward?)

Explanation / Answer

a) From Newton's 2nd Law we have F)net) = m*a = 0.094kg*16.0m/s^2 = 1.504N b) Now we have F(fuel) - m*g = m*a So F (fuel) = m*g + m*a = 0.094*9.8 + 0.094*16 = 2.167 = 2.42N c) Only force acting (neglecting drag) = weight = m*g = 0.094*9.8 = 0.9212N d) At the top of the trajectory the net force is still the weight = 0.921N and the acceleration is -g = -9.8m/s^2

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