Question

Please answer the question and select upward or downard for each part of the question

A model rocket is fired vertically from rest. It has a net acceleration of 15.6 m/s^2. After 1.25 s, its fuel is exhausted and its only acceleration is that due to gravity. The model rocket has a mass of 92.4 g and you may assume the mass of the fuel is much less than 92.4 g. What was the net force on the rocket during the first 1.25 s after liftoff? F^rightarrow = __________ N What force was exerted on the rocket by the burning fuel? F^rightarrow = __________ N What was the net force on the rocket after its fuel was spent? F^rightarrow = __________ N 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? F^rightarrow = __________ N a^rightarrow = __________ m/s^2

Answer 1

(a)

from newtons second law

Fnet = m*a = 92.4*10^-3*15.6 = 1.44 N   upwards

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(b)

Fnet = F - mg

F = Fnet + mg

F = 1.44 + (92.4*10^-3*9.8) = 2.34 N    upwards

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(c)

F = Fg = m*g = 92.4*10^-3*9.8 = 0.905 N downwards

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d)

F = Fg = m*g = 92.4*10^-3*9.8 = 0.905 N downwards

acceleration a = F/m = g = 9.81 m/s^2 downwards