SAT® Subject Test in Physics

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Red and Blue Mass Spring Force


The figure below shows the same ideal spring in three different situations.

First, without a mass hanging, the spring is unstretched.

Next, with the blue mass hanging, the spring stretches.

Finally, with the red mass hanging, the spring stretches twice as much as it did with the blue mass.

How much does the red mass weigh, compared to the blue mass?

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The red mass weighs twice as much as the blue mass.


The red mass weighs four times as much as the blue mass.


The red mass weighs half as much as the blue mass.


The red mass weighs about 1.4 times as much as the blue mass.


We cannot determine how much the red mass weighs compared to the blue mass, because we do not know the unstretched length of the spring.