# Physics

1. In outer space, where there is no gravity or air, an astronaut pushes with an equal force of 20 N on a 3 N moon rock and on a 9 N moon rock. Which statement is the most accurate about this situation?
A. Since both rocks are weightless, they will have the same acceleration.
B. Both rocks push back on the astronaut with 20 N.
C. The 9 N rock pushes back on the astronaut three times as hard as the 3 N rock.
D. Since both rocks are weightless, they do not push back on the astronaut.

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1. both rocks push back with 20 N, however, both are accelerating. The 20 N force is counteracted by the inertia of each rock (inertia=mass) accelerating (ma).

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2. So A?

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posted by Amber
3. no, they accelerate at different rates. B.

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4. They may be weightless but they have mass. It is a bit misleading to say 3N rock. The implication is that it has a weight of 3N on earth where g = 9.8 m/s^2 approximately. That means that the 3 N rock has mass of 3 / 9.8 kilograms or very roughly .3 kg. Then do F = m a for the rest of the problem :)

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posted by Damon
5. Thank you!

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posted by Amber

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