8. a 300g mass hangs at the end of a string. a second-string hang from the bottom of that mass and supports a 900g mass. (a) find the tension in each string when the masses are accelerating upward at 0.700m/s2 . (b) find the tension in each string when the masses are accelerating downward at 0.700m/s2 .

First we need to analyse each mass and all the forces that interact with each of them. To do that, we use a free-body diagram and from that it'll be easier to analyse all the forces and write the mathematical relation between them, each free-body diagram is attached.

Now, we need to find a expression for the second tension and solve the equation.

Now, we replace the second tension in the first equation:

Therefore, with an upward acceleration, the tensions are and .

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Therefore, with downwards acceleration, tensions would be and .

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there are no contact forces mentioned on the list of choices that you've provided.