## Physics (10th Edition)

a) The impulse-momentum theorem states that $$\vec{J}=\vec{p_f}-\vec{p_0}$$ When the plane is flying with a constant momentum, $\vec{p_f}-\vec{p_0}=0$, there is no net impulse acting on the plane during this time. b) We call the thrust force $T$ and air resistance force $R$. We have $$\sum \vec{F}=\vec{T}+\vec{R}$$ $$\sum \vec{\overline F}\Delta t=\vec{\overline T}\Delta t+\vec{\overline R}\Delta t$$ $$\vec{J_T}+\vec{J_R}=\vec{J}=0$$ $$\vec{J_T}=-\vec{J_R}$$ The impulse of the thrust is equal in magnitude but opposite in direction with the impulse of the air resistance force.