Answer #122

The answer is (b): in fact the spring scale will read 163 grams (well, actually closer to 153 grams), as can be seen in a slow-motion mpeg video by clicking your mouse on the photograph below.

Two equations for the motion of this system are:

(M+m)a = mg and T = Ma,

so the tension in the string after the system is released is given by:

T = Mmg/(M+m), or T/g = Mm/(M+m).

Putting in the values of M = 875 grams and m = 200 grams, T = 163 grams.

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