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Following figure is the speed-time graph for a rocket from the moment when the fuel starts to burn, i.e. at time $t=0$.
$(a)$ State the acceleration of the rocket at $t=0$.
$(b)$ State what happens to the acceleration of the rocket between $t=5 s$ and $t=60 s$.
$(c)$ Calculate the acceleration of rocket at $t=80 s$ Give reason for your answer.
$(d)$ The total mass of the rocket at $t=80\, s$ is $1.6 \times 10^{6}\, kg .$ Calculate the resultant force on the rocket at this time. Give reason for your answer.
Solution
$(a)$ No net acceleration, balanced force between burning of fuel and gravitational acceleration.
$(b)$ Increases after $10$ sec, till $t=50$ s; zero acceleration after $50$ sec because it attains constant velocity.
$(c)$ Zero.
$(d)$ Zero as it is moving with constant velocity.
