9. How does a spacecraft leave the surface of the Earth?
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1 point
The spacecraft produced an upward force of thrust that was equal to the downward force of gravity.
The spacecraft produced an upward force of thrust that was greater than the downward force of gravity.
The spacecraft produced a downward force of thrust that was equal to the downward force of gravity.
The spacecraft produced a downward force of thrust that was less than the downward force of gravity.
The spacecraft produced an upward force of thrust that was greater than the downward force of gravity.
The correct answer is:
The spacecraft produced an upward force of thrust that was greater than the downward force of gravity.
To lift off from the surface of the Earth, a spacecraft needs to produce an upward force of thrust that is greater than the downward force of gravity. This allows the spacecraft to counteract gravity and overcome the pull towards the Earth's surface. With enough thrust, the spacecraft can accelerate and eventually leave the surface of the Earth.
To generate this thrust, spacecraft typically use rocket engines. These engines work by expelling high-speed exhaust gases in the opposite direction of the desired motion. Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. So, as the rocket engines expel gases in one direction, the spacecraft experiences a force in the opposite direction - providing the thrust needed to propel the spacecraft upward.
The magnitude of the thrust produced by the rocket engines must be greater than the force of gravity acting on the spacecraft. Gravity pulls objects towards the center of the Earth with a force proportional to their mass. By generating enough thrust, the spacecraft can create an upward force greater than the force of gravity and gradually lift off from the Earth's surface.
In summary, to leave the surface of the Earth, a spacecraft must generate an upward force of thrust greater than the downward force of gravity. This is achieved by using rocket engines that expel high-speed exhaust gases, creating an equal and opposite reaction to propel the spacecraft upward.
10. What are the action and reaction forces at work in this picture?
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1 point
Captionless Image
the book is pushing on the table and the table is pushing on the book
gravity is pulling the book downward
the flower vase is pushing up and gravity is pulling down
friction is pushing up and gravity is pulling down
Without being able to see or contextualize the image, it is not possible to determine the action and reaction forces at work in the picture. Therefore, none of the provided options can be definitively chosen as the correct answer.
2. What will happen to an object in motion if an unbalanced force does not act on it?
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1 point
it will slow down eventually
it will stop
it will keep moving at the same velocity forever
its speed or direction will change