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Question

Explain Newton's Laws of Motion with an example.

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Solution

Newton's First Law: "Every object persists in it's of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it."
Applied to rocket liftoff


Before firing:
The object in a state of rest, airspeed zero.
Engine fired:
Thrust increases from zero.
Weight decreases slightly as fuel burns.
When Thrust is greater than weight:
Net force (Thrust-Weight) is positive upward.
Rocket accelerates upward
Velocity increases

Newton's Second Law
Differential form: Force = change of momentum with change of time
F=d(mv)dt
or:
Force= change in mass \times velocity with time
F=(m1V1m0V0)(t1t0)
With mass constant: Force=mass×acceleration F=ma
Force, acceleration, momentum and velocity are all vector quantities. Each has both a magnitude and a direction.

Newton's Third Law: For every action, there is an equal and opposite reaction.
Rocket Engine Thrust



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